Only a few minutes of sleep is not going to rejuvenate you for the rest of the day. School is a place dedicated for learning. If you're not getting enough sleep at night, that's on you. Learn how to prioritize your time effectively and finish tasks efficiently. If you still aren't getting enough sleep from the overwhelming amount of homework and studying, then don't do some of them. Getting good grades is important, but your health is far more important, especially your mental health.
This is because not all students can sleep at night .This could be due to family problems,electricity issues or any other problem.And even if students did sleep at night then allowing them a 15 min nap will allow them to be more fresh and hence more likely to learn and comprehend new information.Some students also sleep during lectures and hence miss them .Hence it is better if sleeping is allowed as it will result in exuberant students willing to learn