Clue: Top one of 15 is one of 15 (4)
Answer: LION
Explanation: Definition: one of 15
I think that the first 'one of 15' refers to the theme, which, with a little goodwill, indicateses 15 musicals, of which the LION King is the 'top' grossing so far. Does the SUPERBOWL count as a musical?