If you're close to your true 12-15 RM for a lot of exercises, then I'd move on to the 8-10's. Whatever's still lighter than it needs to be, make adjustments and increases for your 8-10's. My growth didn't start till the last week of 15's on through the rest of the program. I'd try to milk the 8-10's for three weeks, then the 4-6 reps indefinately.. Your work capacity/fitness level will be increased from all the high reps.
If you aren't gaining by the 8-10's, then the blame rests solely on your undereating. By this point, you have the benefit of frequency, progressive loading, and good exercise selections. That means there's only one thing left to blame..