Level up 3 Characters to Level 15.

You level you characters in Disney Infinity by collecting Sparks (blue objects found from defeating enemies and breaking objects in the world). You also gather sparks from completing quests in the play sets and winning medals in the Adventures. Completing each of the 3 starter play sets should level that character to somewhere between level 8 and 12 (depending on which play set and how many of the side quests you complete).

The quickest way to level to 15 after this is to select the Castles and Slingshots Adventure and continue getting a gold medal on it until you hit level 15.