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.
And, wouldn't you know, that's exactly what happened. I did reach the goal, but with an asterisk. I was in the middle of a run on a rainy day when the sleeve of my jacket must have hit the watch face just right that it swiped right, tapped add workout, tapped elliptical, and started counting an elliptical workout. I had no idea at the time what happened so I stopped the workout, started a new run workout (on the watch - I was still running), and, of course, immediately turned on water lock.