Battery is a 7.6V 2100mAh lipo
Yes, that is a lot of spark for this plane. You would get away with a battery that is 10-15% of this capacity.
Are you planning on running a brushless motor on it somewhere?
I used a 300 mAh NiMH on my simple P51 and I could fly it all day without worrying about it losing charge. After all, it only had to drive 2 servos.