Metta World Peace has decided on wearing his father’s high school number at Long Island City High — 51. World Peace had wanted to wear 15, which he donned at St. John’s and with the Lakers, but it has been retired by the Knicks twice for Earl Monroe and Dick McGuire. “My dad is the reason I am tough,’’ World Peace wrote in a text message to The Post. The 6-foot-2 Ron Artest Sr. played small forward for Long Island City his junior year in 1974-75. Prior to that, he played for the junior varsity at John Bartram High in Philadelphia, the same school Monroe attended. “I’m very happy about it,’’ Artest Sr. told The Post. “It’s icing on the cake for him to wear my number. It would be even more icing on the cake if he won a championship. But at least now I can see him play in person every game.”