If you are not suffering or very uncomfortable physically or emotionally due to the size of your chest, you should not get a breast reduction. I would be shocked and angered if any doctor would try to convince you to have this surgical procedure at your age - you haven't even finished growing - unless he deemed the size of your breasts was a serious medical or psychological problem. You are the only true judge of that and you should say "No" on both counts.
Please try to get a trusted female family or extended family member or friend to talk with your mother about her concerns. It would be great if you and your mom could see a family therapist to talk about these issues. Perhaps you could speak to your regular doctor, in confidence, and ask for his help in handling the situation. He may choose to be your advocate and try to work things through with your mother.