question about brushless motors

Hi, I have a hopped up e-maxx, @1200 into it, it has a Novak 4400 brushless and running 2 3300 Nimh packs with Dean's I am only getting @ 10-15 min of run time, Is this Normal? I also have a Mini Lst with a 8000kv Mamba and a 8-cell pack and I am getting more like a 1/2 hr on the lst. I am just wondering if it is the Novak Setup, or would it be worth it to go to a mamba max for the E-maxx?, Right now the emaxx wheelies on demand and is fast!, but I would just like to get longer run times, Anyone have info?