Skarners passive in ARAM

Skarners passive seems too overpowered in aram.He can practically keep his crystal passive up as much as he wants making him practically invincible since there is little to no counter play in controlling against his crystals which are placed practically everywhere in the map to let him fully utilize it. Personally the 15 sec disable of taking a crystal should be increased or something similar so that skarner actually be properly played against without his crystal buffs. PS This is my 1st post in the boards Thought I write about this since I didnt find anything similar in the boards