Look at it as relative to your own training level. Try 10-20% more than you would normally do for total sets, and see how you respond. You need to adapt you workload to your previous experience and the time you have. Based on your schedule, doing 10-15 sets per body part would be impossible. You would be at the gym way to long. For me personally, I try to get in and out within an hour, which means something between 20-30 work sets (when you factor in changing exerices, weight, etc). I move that volume up or down depending on my ability to recover and focus,I am only working 1 body part as compared to my whole upper or lower body, rep range, etc.
The key is personal experimentation. Keep good logs so you can determine what is the right volume level for you.