Dude you're 15, I wouldn't worry about it excessively. It's related to puberty in my opinion. I had the same problem around that age and it lasted at least a year but probably longer. I had lumps under the nipple and if anything pushed into them, like if I were to lay against something, they would hurt. After puberty was finished it cleared up.
What's the bodyfat percentage?
Losing fat will always make the puffiness less noticable bro