I wouldn’t expect it to be 15 minutes from each class each night - more like a weekly assignment from each class that means each night you do 1 hour of one clas

I wouldn’t expect it to be 15 minutes from each class each night - more like a weekly assignment from each class that means each night you do 1 hour of one class, half an hour each of two others, rotating. For many classes though, 15 minutes/night would be very useful. Language learning, for instance, or music practice. Most kids would benefit from 15 minutes of writing prose for any reason, and I think even high school math topics could provide 15 minutes of worthwhile practice questions each evening. All of these are things that you get better at with repeated practice.