15 Dec is in December.
Archaeologia Volume 35 1853 XXXIII. On the 15th of December  the Queen (age 62) was visited by the Countess of Pembroke (age 40), who passed the entire day with her; and, from the frequency of her subsequent visits, it would appear that she was one of Isabella's closest friends. And, again, what can we infer but a clinging on her part to the memory of her lover, when we find that this lady, widow of Lawrence Hastings, Earl of Pembroke, was none other than Agnes, daughter of Mortimer himself; and that we thus have recorded visits received by Isabella of a daughter, the grandson, and grandson's brother-in law of her favourite, within the space of one month?
On 15 Dec 1357 Gerard Lisle 1st Baron Lisle (age 53) was created 1st Baron Lisle of Kingston Lisle in Oxfordshire 3C 1357.
On 05 or 15 Dec 1392 Alexander "The Wolf of Badenoch" Stewart 3rd Earl Buchan (age 49) and Euphemia 6th Countess of Ross were divorced.
On 15 Dec 1455 the Courtenay family, Earls of Devon since 1355, and Bonville family resolved their differences at the Battle of Clyst Heath. Thomas Courtenay 13th Earl Devon (age 41) defeated William Bonville 1st Baron Bonville (age 63). Battle something of an over-statement; the number of dead reported by one chronicler as being twelve. Following the battle the victorious Courtenay's attacked Bonville's Shute Manor.
On 15 Dec 1470 John Valois Anjou II Duke Lorraine (age 46) died at Barcelona.
On 20 May 1561 John Eyre died. On 15 Dec 1558 Margaret Blennerhasset died. They were buried in All Saints Church Narborough [Map]. Brass. The inscription on the brass says "Here do lye John Eyer Esquire late Receyvor Generale to Elizabeth the Quenes Majestie, in the counties of Norf., Suff., Cantabridge, and Huntyngton, and one of the Masters of her High Court of Chancerye and Margaret his wyfe, one of the daughters of Sir Thomas Blenerhaiset of Frens Knight late Wyfe of John, Spelman Esquire, son and heyre apparent of Sir John Spelman, Knyght." Armorials top left and middle Quartered Eyre Arms and Townshend Arms with a crescent difference, top right Quartered Eyre Arms and Townshend Arms impaled with 1&6 Blennerhassett Arms, 2, Argent, three Escutcheons Sable: LOWDHAM 3 Gules a Pall reversed Ermine: KELVEDON or KELDON 4 Azure a Lion rampant Argent crowned Or: ORTON: 5 Azure a Fess between three Fleurs-de-lis Or: SKELTON.
John Eyre: After 27 Dec 1545 he and Margaret Blennerhasset were married. Her second husband.
Pepy's Diary. 15 Dec 1664. So to the Coffeehouse, where great talke of the Comet seen in several places; and among our men at sea, and by my Lord Sandwich (age 39), to whom I intend to write about it to-night.
Pepy's Diary. 15 Dec 1666. Good news to-day upon the Exchange [Map], that our Hamburgh fleete is got in; and good hopes that we may soon have the like of our Gottenburgh, and then we shall be well for this winter. Very merry at dinner. And by and by comes in Matt. Wren (age 37) from the Parliament-house; and tells us that he and all his party of the House, which is the Court party, are fools, and have been made so this day by the wise men of the other side; for, after the Court party had carried it yesterday so powerfully for the Paper-Bill1, yet now it is laid aside wholly, and to be supplied by a land-tax; which it is true will do well, and will be the sooner finished, which was the great argument for the doing of it. But then it shews them fools, that they would not permit this to have been done six weeks ago, which they might have had. And next, they have parted with the Paper Bill, which, when once begun, might have proved a very good flower in the Crowne, as any there. So do really say that they are truly outwitted by the other side.
Note 1. It was called "A Bill for raising part of the supply for his Majesty by an imposition on Sealed Paper and Parchment" B.
On 15 Dec 1681 James Compton 3rd Earl of Northampton (age 59) died. His son George Compton 4th Earl of Northampton (age 17) succeeded 4th Earl of Northampton 5C 1618, 5th Baron Compton of Compton in Warwickshire.
On 15 Dec 1713 Welbore Ellis 1st Baron Mendip was born to Bishop Welbore Ellis (age 62) and Diana Briscoe.
On 15 Dec 1768 George Devereux 13th Viscount Hereford (age 24) and Marianna Devereux Viscountess Hereford were married. They were third cousins?
On 15 Dec 1785 King George IV of Great Britain and Ireland (age 23) and Maria Anne Smythe aka "Mrs Fitzherbert" (age 29) were married. The marriage was invalid under English civil law because his father had not given his consent. Her uncle Henry Errington and her brother John Smythe were witnesses. The ceremony was performed by one of the prince's Chaplains in Ordinary, the Reverend Robert Burt, whose debts of £500 were paid by the prince to release him from Fleet Prison [Map]. He the son of King George III of Great Britain and Ireland (age 47) and Charlotte Mecklenburg Strelitz Queen Consort England (age 41).
On 15 Dec 1841 John Fane 10th Earl of Westmoreland (age 82) died. His son John Fane 11th Earl of Westmoreland (age 57) succeeded 11th Earl of Westmoreland 2C 1624. Priscilla Anne Wellesley-Pole Countess of Westmoreland (age 48) by marriage Countess of Westmoreland.
On 15 Dec 1849 William Henry Holland 1st Baron Rotherham was born.
On 15 Dec 1869 James Lindsay 7th Earl Balcarres 24th Earl of Crawford (age 86) died.
On 15 Dec 1886 William Charles Evans 8th Baron Carbery (age 74) and Victoria Cecil Baroness Carbery (age 43) were married. The difference in their ages was 31 years. She the daughter of Brownlow Cecil 2nd Marquess Exeter and Frances Isabella Selina Poyntz Marchioness of Exeter.
On 15 Dec 1898 George William Henry Venables-Vernon 7th Baron Vernon (age 44) died. His son George Francis Augustus Venables-Vernon 8th Baron Vernon (age 10) succeeded 8th Baron Vernon of Kinderton in Cheshire.
On 15 Dec 1898 William John Legh 1st Baron Newton (age 69) died.
On 15 Dec 1907 John Lyon-Dalberg-Acton 3rd Baron Acton was born to Richard Maximilian Lyon-Dalberg-Acton 2nd Baron Acton (age 37).
On 15 Dec 1908 Lt Colonel Hugh Annesley 5th Earl Annesley (age 77) died.
Salisbury Cathedral [Map]. On 15 Dec 1922 Lieutenant General Sir George Montague Harper (age 57) died in a car accident when his car skidded and overturned fracturing his skull. Memorial in Salisbury Cathedral [Map] sculpted by Allan Gairdner Wyon (age 40).
Lieutenant General Sir George Montague Harper: On 11 Jan 1865 he was born.
On 15 Dec 1944 George Hobart-Hampden 10th Earl of Buckinghamshire was born to Cyril Langel Hobart-Hampden (age 42).
Charles Strathavon Heathcote-Willoughby-Drummond: On 18 May 1870 he was born to Gilbert Henry Heathcote Drummond Willoughby 1st Earl Ancaster (age 39) and Evelyn Elizabeth Gordon Countess Ancaster (age 24). On 09 Jan 1907 Charles Strathavon Heathcote-Willoughby-Drummond (age 36) and Muriel Agnes Stuart Erskine were married. She the daughter of Shipley Gordon Stuart Erskine 14th Earl Buchan (age 57). He the son of Gilbert Henry Heathcote Drummond Willoughby 1st Earl Ancaster (age 76) and Evelyn Elizabeth Gordon Countess Ancaster (age 60). On 15 Dec 1949 Charles Strathavon Heathcote-Willoughby-Drummond (age 79) died.