Big boobs

I’m 15 and have g size boobs!! It’s insane I’m bigger then my mom and all of my friends. My back constantly hurts and I have really bad posture. I’m not skinny but I also feel like I’m pretty average. Im about 140 pounds maybe a little less. And I know if I get a breast reduction now that they will probably grow afterwards. I am beginning to exercise and eat better to see if I can loose weight in my boobs. I just feel like for me being an average size, like I weigh the same as my friend with a cup boobs and we have similar body types, that g is huge! What can I do? I wish they were smaller!