Efficient 15 minute routines

So here's the dilemma I am currently in. I work 6/12s and am home roughly 1-2 hours a night that I'm awake. I've been trying to sneak in about 15 minutes of exercise in the evening before taking my shower and heading to bed. I'm assuming most people will direct me to the RR but was hoping to pare it down a little bit for my allotted time.

My current routine is 3-5 sets of 10 of squats, incline push ups until I can do 10 regular and sit ups. I don't really have any equipment to use but was wondering if there was any more movements I could work on or alternate between?

My big concern is being unbalanced or only working a couple of muscle groups and then these being tired and not recovering but I'm trying to make a change with the time I have. I also sneak in a 30 minute walk with the dog some nights when time allows and if they haven't already been out without me.

Thanks for reading and any suggestions!