Hi. I agree with Ruth.
1. Do not let yourself be maneuvered into a situation where you are alone with him.
2. Tell your instructor immediately. Also, if you have a good relationship with your mom or dad, and they won't just go ballistic and pull you from training, tell one one of them.
3. Most people like this are like bullies: they back off if firmly confronted. If you think you can do it: Direct eye contact, a level voice, good posture: I am 15 years old, I do not like being spoken to this way and you will stop it NOW. Don't be afraid if others hear this--it is all the better. It embarrasses him, not you! It's also ok if right now you feel you can't try this. Main thing is to let other, responsible adults know and get them to deal with it.
I remember being your age, and how isolating it could feel when somebody was like this jerk. Do reach out for assistance in dojo (and home if ok) and do let us know.