Asoccer club has 15 players for every team with the exception of two teams that have 16 players each is the number of players proportional to the number of teams

No, the teams are not proportional to the number of players.

Their kid-to-team ratio must be the same.
For future reference, think of fractions. In the following example, the number of teams are on top and the number of kids in the said teams are on the bottom. 

1/15=2/30
But 1/15 does not equal 1/16

The correct answer will be d. -4