RE: The new electric YAK 54 from Greatplanes!
Yes, I would say that is normal at full throttle with those packs. It's all about how much amperage you're pulling with that engine/battery/prop combo. Do you have a Wattmeter to hook up inline between the battery and the ESC? I don't have one of those engines, but at full throttle with a 10-4 APC "E" prop I'm pulling about 34 amps. I don't need anywhere near that amount of power to keep it in the air, so my 2100 maH batteries easily last 10 minutes.
Another thing you can do with some of the ESCs is to program them for a "soft" cutoff, so they modulate the power down when the battery voltage gets close to 9v. Then you have some warning and don't have to dead stick it in.
Some ESCs also have a "brake" feature, where I believe they use battery voltage to keep the prop from windmilling when the throttle stick is all the way closed in flight. This would be a drain on the battery and would shorten your flight time. Usually this can be programmed out.
It's real important to know how much amperage you're pulling when using lipo packs---too much and you can at the very least wreck them, or at worst they'll catch fire.
Good luck.