General fact: 5215 is a number for which we're missing a fact (submit one to numbersapi at google mail!).
Mathematical fact: 5215 is a boring number.
Trivia: 5215 is an unremarkable number.
Historical date: April 11th is the day in 2001 that the detained crew of a United States EP-3E aircraft that landed in Hainan, China after a collision with a J-8 fighter is released.