My Hobbistar was a great plane. My friends were all blown away how fast this plane flew.
Anyway, I could routinely get 15-18 minutes of flight out of mine. It will get better when you get it broken in. You do have to get it tuned well though. If you have it running too rich it will blow a lot of unburned fuel out the exhaust. The 65 LA is a great little engine and they aren't to hard to get running right. If you get an experianced person to help you tune it it might help.
Do you fly at full throttle the whole time you are up?