First if you goal is to build muscle mass I would consider one change to your routine. Either drop the leg curls and add in Sumo Deadlifts (they will also hit the hamstrings) and Deadlifts are IMO the best of all mass building exercises, even better than Squats. Or if you think Deadlifting and Squating is too much for one workout then alternate between Squats and Deadlifts. Really it would be fine if you didn’t Deadlift this cycle as long as you do Squat but the sooner you add them in the sooner you will get the benefits of them. Yes if doing 2x15 you can move to 2x10 and 3x5, however don’t be surprised if when you get to the very end of the 5s if 2x5 is all you can manage. It’s ok to let the volume drop once the weights get really heavy especially since you’re going to be working out 3 times a week. Just listen to your body and if you feel you’re not recovering between workouts cut back a little bit. It’s fine and probably beneficial for recovery to do something like basketball on rest days as long as you don’t overdo it. Also remember to keep you calories up to account for the extra work. I find that doing hill sprints gives me a great cardio workout and also helps my lower body recover from intense workouts.