Here in San Antonio, 15 is the age when many of our daughters have their quinceañera. 15 is the first score in tennis. It is triangular, pentagonal, and pentatope simultaneously.
The 15-puzzle is a 4x4 grid with 15 movable pieces and one missing piece. The game is solved when all fifteen numbers appear in order.
15 is the number of seasons of coaching (assistant and head coaching) that Gregg Popovich had under his belt before taking over as the head coach of the San Antonio Spurs. He served as an assistant coach for six seasons in the Air Force, eight with Pomona-Pitzer as head coach, and a year under Larry Brown in Kansas.