It was realy hard but finaly I finished the challenge campain with Level 57 and 2x 4* and 2x 5* heroes. I did it with the goblin Team. But I realy want to know If somebody did this faster and what Team he used. I realy had problems with pure fire levels and "dark" enemies. Because of the Level difference I could not aply and debuffs in the enemies.
I realy think that with a good team it is possible to do it faster.