Im 16. i sleep for 12-15 hours daily and when i am wake i have severe fatigue. this has gone on for several months. is there a problem?

Fatigue: yes there is. You may have a sleep disorder, an endocrine disorder such as hypothyroidism or anemia. It would be s good idea to get a good physical along with labs and other evaluations as indicated

Im 16. I sleep for 12-15 hours: It could be a problem. There can be many causes , such as Mono( common at your age), metabolic disorders such as hypothyroidism, diabetes or anemia Another possibility is could be a subtle depression, where fatigue, either sleeping too much or not sleeping well, moody, + appetite irregularities are seen in depression.. Recommend seeing a doctor , at least for lab work , and exam if this persists.