I've tried a few times, and I'm confident Zhalk can be taken down in the given time.
(I don't use barrels, by the way. It doesn't feel right to me. I also don't plant someone by a restoration thing outside the helm. That also feels a little like cheating.)
*
But getting Zhalk, the mind flayer, and the two cambions in 15 turns? I haven't managed to do that yet, and I'm not sure I'll be able to in that timeframe without resorting to (what I consider to be) questionable tactics.
