If at all possible try and lose some weight, because my cousin went through the same thing. She was extremely large chested. My entire family on my mothers side is infact. Everyone has AT LEAST 40DD sized bras and generally that's because that's the largest bra they can find but their breasts are actually larger. My cousin had to get special bras made because her cup size was roughly between a g-I. (aka HUGE). At 15 she went for a reduction because it was causing so many issues with her back, shoulders etc. Things were great, but because she was still in the middle of puberty they came back. Infact they came back and are now larger than before her reduction.
So your best bet is try and lose some weight and see what happens. You may lose some of the size in your chest without major surgery with all the pain and recovery time. But give it time, if you wait till you're a little older you may not have the problem my cousin had and have to consider going through the surgery twice.
Surgery is far from the only thing that will cause a change in bust size. If you lose weight, you will also lose your bust size. What about that isn't a help?
If you really would prefer (or for some reason think) surgery is the only way to go, you don't have to lose weight. But know that if you have a reduction done and then lose weight, your chest size will also likely decrease drastically. I lost 60 pounds after I had my daughter, and my chest is currently almost non-existent. Before I got pregnant I was a B. Now I'm the smallest A size, and usually don't even need a bra. Nothing to contain.
Breasts are basically just fatty tissue, so if you lose weight, your breasts will decrease in size as well. What are you doing to try and lose weight?