Maybe it helped that I didn't watch a video of the battle? :)
Added 5 minutes later
You'll laugh, but I won on the second try as well. The titans got stunned once near the end, but the snipers also got lucky twice. The wizard cast an air shield at the right moment (after all the titan blockers died). He didn't cast haste even once. There was 1 wizard and 9 snipers left.
Added 5 minutes later
Ah, I was just told that it's not just about winning, but also about minimizing losses...