As a 15-year old who gets 6 hours of sleep, should I be getting more sleep?
As a general rule of thumb, those who think they have the DEC2 mutation usually do not have it. The reason for this is due to wishful thinking.
That being said, until you go have your genome sequenced and empirically check for the mutation, it's always a possibility.
If you are really curious you can take some preliminary data on yourself. Record when you go to bed/ when you think you fell asleep and when you wake up for 3 weeks to a month. If your sleep cycle is fairly regular - going to bed and rising at the same time - and you feel energized throughout despite only getting 6 hours of sleep, you have some good data on your sleep habits that may indicate that you are a more efficient sleeper.
If, however, you go 3–4 days with 6 hours of sleep, then regress to a night of 8–10 hours of sleep, it means you've acquired a sleep debt and you've exhausted yourself. Even if the majority of nights you get 6 hours of sleep, if there are any unplanned interruptions in your sleep cycle throughout the 3 weeks, you're probably one of those wishful thinkers.
As an aside, my mother got a call from health system run by the university here. We weren't surprised to discover she does have the mutation: Back in her day, regulations on the number of hours surgical residents could work in a shift were significantly more lax. She was often awake and operating for 72 hours straight.