What Horton said! Moving around on the ski to get it to do something is not the most efficient way. To me, if your stacked position is pretty good, it could indicate one or a combination of several things are happening- wrong ski/length, incorrect binding location or tuning issues. I forget where I first heard it (and they were no doubt quoting someone else) but paraphrased- "There is one 'best' skiing position (for you), and there are two turns"... The 'weighting' changes happen kind of automatically, based on accelleration, decelleration and skier path more than anything else.
Another 'nugget' various coaches have yelled at me about is that if the line is too tight at my turn apex, the ski can not finish and have usable angle. Meaning too that I did something wrong well before that turn and needed to 'create space' first.
15 off is a pass where the boat is well out in front of you at the buoy, and you are not easily getting, 'free of the boat'. Try skiing it like a shorter line pass- work hard spray to spray, and keep your ski position, with the handle in and down on a turning edge,until you are out to buoy width, then release and finish the turn. You will get space and wont need to move around on the ski much at all.