instead of doing 2 or 3 sets of an exercise why not pick an exercise for a certain bodypart lets say legs, and starting on your 15s for squats just keep doing sets till you know you wont get out another set.... then move onto chest and do the same there ...then back shoulders etc..everyone keeps saying that if you can handle more sets then go for it, this way you would only be doing 1 exercise per bodypart then moving on