M.P.
haha that happened to me too but earlier than at 15m. Now my son is 18m and still nursing and I make so little milk that it doesn't show much if it's uneven.
#1 I'd say is call la leche league because they're just awesome. But from my own person unqualified view here's my advice: ;)
The LLL people told me when I tried to wean my son that sometimes when you try to wean before the baby decides to wean, it becomes worse because the baby senses that it's being taken away so he wants it more. So I decided to stop trying and it's worked. He nurses much less now. I think it'll come out naturally.
I think that if you take it easy, he'll just nurse leeeess and then if ther eis a difference in your breast size it won't be so obvious because there isn't much milk in there anyway. Plus you'll both be happier because it sounds like you don't really wanna wean anyway, you're just doing it to solve this problem.
Another idea is you can always do pectoral exercises and lift weights and stuff to pump up the muscles behind your breasts. Then the muscles will (which are even) be more noticable than the breast tissue (which is uneven).
Lastly, if you have any discomfort the size difference could be a result of a breast infection or clogging. Check to make sure it's not hot to the touch or sensitive or clogged. You didn't mention that so it's probably not the case but I thought I'd throw it out there.
