LordLinux- On both Angiosphere1 and PTR X3 (LordLinux1 on PTR X3)
1) It is oft said "Nero fiddled while Rome burned". Nero was the Emperor at the time, and he was born on December 15th. = XV in Roman numerals.
2) Domitian was the ruler that reigned for 15 years (XV again!), at odds often with the senate and seen a a successful but authoritarian ruler.
3) Probably the most commonly know, at least by name, Julius Caesar wrote the Commentary on the Gallic wars, and he was born March 15! (XV)
4) Nicknamed "Germanicus" to distinguish him from the former Emperor Julius Caeser, he was considered morally and physically superior, and was thought to have been poisoned by his Uncle or adopted father during an expedition to Egypt. He was born on 24 May 15 BC - (15 = XV !).
5) Hmnnn...a difficult one to research. Gaius Scribonius Curio (d. 49 BC) was the son of Gaius Scribonius Curio. (Same name "Gaius") He was a friend to Pompey, Julius Caesar, Mark Antony, Clodius and Cicero. He was known as a distinguished orator. Curio's character was very conspicuous and profligate. Despite his faults, Cicero assisted him in every way and evidently wrote several letters to him. Gaius Scribonius Curio Burbulieus (the senior) (d. 53 BC) was a Roman statesman and orator. He was nicknamed Burbulieus (after an actor) for the way he moved his body while speaking. Augustus was born Gaius Octavius Thurinus into an old and wealthy equestrian branch of the plebeian gens Octavia. His maternal great-uncle Julius Caesar was assassinated in 44 BC. Since all three were related to, or ruled under/governed under Julius Caesar, who was assassinated on the "Ides of March" (March 15, or March XV, 44 BC), I believe that the "Ides of March" is the common denominator (15 = XV) here.