Leveling heroes in this game actually hurts you. My heroes used in the raid (Hal, Saarvin, Tommus, Cori) are level 17 (Cori is 16) and all their gear is level 15-16. I was able to clear 8-15 rooms per key, depending on when the sword drops occured. OP, your gear is close to the same level as mine, but your heroes are 5 levels higher so the raid scaling will be exponentially more difficult. If I could go back, I would leave all my heroes at level 15 and just increase their gear, otherwise the raids and rallies get way more difficult.
It’s a shame that the game penalizes you for leveling your heroes, but I think it’s a money-making scheme. Players think their heroes are more powerful the higher level they are, but then they get frustrated so spend real $ to improve their heroes, only to level them up too fast again and repeat the cycle.
As another example, I was in a battle against a player with level 9-11 heroes against my level 15-17 heroes. My gear is level 15-16 and I got my butt kicked. This wasn’t some cheezy dominate/stun/disarm battle either, the other player did crazy ammounts of damage and was one-shoting my heroes.