31 workouts of 15 minutes or more for me. It probably will not happen because I deliberately do not workout on Christmas Day - it's one of my two that I always take off (Mother's Day is the other.) But I will probably get 30 (barring illness or severe injury.)
You could always end a workout and start a new one in the middle. You could even do 31 15 minute workouts in one day, Apple isn’t picky on this particular metric.
Two things about these challenges. One - I don’t care all that much if I make it or not. I exercise MORE than enough. Two - I never cheat just to complete it. I’m more interested to see what the challenge will be than whether I actually reach it.
Read a novel.
How is working the system considered cheating?