Not sure what the final verdict is whether this LoL level 15 is "officially" bugged, but I'm grinding it with success.
Here is my 2 cents on the topic.
-Auto-Grind Team-
Hallowed Ed- Orbit
Killer Prime- Greed/ Warlord
Major Malakhov- Singularity
W. LoL (Maxed)- Vipers/T3 Cosmic
*This order kept them healed better than any other variation.
*Tapping Lucy (to focus attack) helps but is not mandatory.
* This is not a 100% survival, but best I've seen thus far (95%.)
* The Red Onyx twins in stage 1, seemed to be the biggest obstacle.
*Out of the 3 LoL keys grinding 15, I got (4) Max Awakening shards.
Good Luck!