Stick with it.
If you can get 20 years in, then you have the medical benefits which go with a military retirement in addition to some additional retirement pay.
The financial cost of going the civilian route compared to the military flight training is substantial. If you go civilian, you'll have to get to 1500 hours before you get an ATP vs. 750 and the R-ATP.
The quality of your training will be greatly impacted by the military background and training. Military flight training will provide you a better foundation with respect to systems training. Being in the KC-135 will give you better experience in the crew environment than civilian flight training will. Networking through your unit is invaluable.
Good luck!