A 7.4v battery with standard 18:1 gears and a standard G&G motor will be a bit sluggish.
The G&G ETUs are designed to work with higher voltage batteries; the best thing to do is to swap the board for the Perun ETU++. Not only is it better quality and works with 7.4v batteries, but you also get adjustable precocking.
I'll add my voice to the choir, from personal experience with the CM16 series with the ETU. 11.1v LiPo is definitely the best choice; 7.4v will work but you will notice the difference for the worse.