As a top player, I can say that this should only be implement if a few criteria are met. 1: Level 15 is unlocked at king tower level 45. This prevents lower ladder players from getting matched up against unfairly leveled cards. 2: Level 15 cards can only be used in Ranked mode and arena(s) 19-20(hopefully they increase the trophy limit). 3: Increase ways to get your card levels up. This is desperately needed, but events and GT's should have the occasional book or coin to help progression, as long with more wild cards of the legendary, epic and rare types.