No doubt. I know many people in the area with Projetis running Mega 16/15/3 motors. They're using CP1300 NiCd packs, which are VERY robust, and those come out HOT HOT HOT! I'd imagine those relatively tiny NiMH cells would go thermonuclear

The long and short of it is, you're drawing way more Amps than the battery can handle. You've got several alternatives to get things tamed down:

1. Gearbox and a larger prop.
2. Smaller direct drive prop.
3. Fewer cells.
4. 16/15/4 or 16/15/5 motor.

The 2-cell LiPoly will have the effect of #3, being closer to 7 NiMH cells in practical applications. However, you don't specify the brand and model of the pack(s) you have. That's VERY important. One manufacturer's "2000mAh LiPoly" might be able to hold up to the abuse, while another will overheat and turn into a lithium sausage inside your airplane, possibly catching fire in the process. Yours need to hold up to 30 Amps. Look at the "C" rating on the pack. Multiply the C rating by the capacity of the pack to get the maximum Amps it can handle. You're looking for a pack that's rated for at least 15C.