You can also keep them all if you like, just alternate squats and deads, flat bench with incline bench, maybe even your CG bench with the military presses. It's sort of what I do, hitting each muscle group 2 ways, but not in one workout, so I can hit them pretty hard.
I don't think it matters in the 15's if you're just doing one set. I do 2 sets minimum of anything I do, so it matters. It also depends upon your recovery abilities. You'll have to pay attention to things as you feel them out, cycle by cycle and KEEP THEM LOGS!