Yeah they are good at regulating themselves, meaning they will not just keep eating mice until they pop. You will find it turns out to be about the amount that would equal a good sized rat for the snake.
The really frustrating ones are when they will stop at one or two, no matter what, then you have to try to feed more often.
For the person who decided to negative rep my previous post, how about you come here and actually explain why my comment is "over feeding"?
15% is a guide-line, like a lot of things that we do. IMO it is difficult to over feed a growing ball python, as long as you are not power feeding or force feeding it. They will eat until they are full then that is it.
For the OP, I have a female mouser who, while a bit annoying, is growing up great and has made it beyond the 1000g mark with no problem. Did she do it as fast as a rat eater? No. But, she has had steady growth.