Could it be healthy to sleep 1hr30min in the afternoon on school days when you're 16.?

It could be.: If you're only getting 7 hours or so of sleep per night, which would probably be typical for a teenager in school, you are not getting enough sleep and are making up for it with a nap. If you are getting enough nighttime sleep, however, excessive daytime sleepiness/napping could be a sign of a sleep disorder such as narcolepsy, or even sleep apnea. If this is the case, talk to your doctor.