My parents have joint custody and i'm 15 years old.
he lives in missouri and she lives about 20 minutes away in kansas.
he wont let me move to my moms house but... like i said they have joint custody... he cant make me stay can he?? hes always threatening to take her to court if i try to move over there... help?

No, YOU do not have a choice.

If you live with your Dad, and your Mom wants custody, she needs to petition to modify the custody agreement. If you move out to live with your Mom before the custody order is modified, then yes, Dad can take her to court.