March 15 is the 74th day of the year (75th in leap years) in the Gregorian calendar. There are 291 days remaining until the end of the year. In the Roman calendar, March 15 was known as the Ides of March.
- 44 BC – Julius Caesar, Dictator of the Roman Republic, is stabbed to death by Marcus Junius Brutus, Gaius Cassius Longinus, Decimus Junius Brutus and several other Roman senators on the Ides of March.
- 1783 – In an emotional speech in Newburgh, New York, George Washington asks his officers not to support the Newburgh Conspiracy. The plea is successful and the threatened coup d'état never takes place.
- 1952 – In Cilaos, Réunion, 1870 mm (73 inches) of rain falls in a 24 hour period, setting a new world record (March 15 through March 16).
- 2004 – French President Jacques Chirac signs the law on secularity and conspicuous religious symbols in schools, commonly known as the headscarf ban.