you are 15 and you are 6'1 254? damn nigga.. u big as hell.
I agree with you though.. forced reps is where its at. And I always go to failure on core lifts. I don't have a certain rep amount that I am shooting for. My first set I am going to pick a weight I can do 12-15 times and rep it until failure. Then add more weight and do the same thing.. and have some drop sets on the last sets.
But that is what works for me, and I have success lifting that way for years.. both when cutting and bulking. everyone is different.