Everyone has a different tolerance for volume in terms of sets. In that case, you should be instinctive in how many sets you do. When doing fifteens, 1-2 sets is enough being your total voulume (if you are doing total body) will be high. As you progress through the fives, you may find it beneficial to do a few more sets (3-4) and maybe decrease number of exercises too to make up for the increased volume. Just a thought. Personally, I do 4 sets on compound movements like squats, bench, rows...and 2 sets on isolation exercises such as lateral raise, bis, and tris.
