15 days post op. Why do 515cc saline look so small? Could they be deflating? (photos)

I am sorry to hear about your concerns. At 15 days post op, you are in the very early stages of healing. Your breasts appear to be sitting high on your chest, which is normal at this stage, however this is what is causing them to look smaller. Once your implants begin to drop and settle, you will have a better idea of what your final result will look like. This process can take anywhere from a few weeks to a few months. If you are concerned with the progress of your recovery, I recommend reaching out to your surgeon to discuss ways to encourage the breasts to settle such as massage or the use of a surgical bandeau. Best wishes for a successful recovery.

Dear rmarin820,I understand your concern and it is quite normal to be concerned about the outcome following a breast augmentation surgery. However, you are still in the very early stages of the healing process at 15 days  post op.Your will need to be patient at this moment and follow what your surgeon has instructed you to do post operatively.At the early stage of the healing process, the tissues around the implants are still swollen. Once the swelling subsides and the implants drop to their final position, you will be able to see the final result of your breast augmentation surgery.Daniel Barrett, MD
Certified, American Board of Plastic Surgery
Member, American Society of Plastic Surgery
Member, American Society of Aesthetic Plastic Surgery

Your implants are pressed flat by your muscle giving the illusion they are smaller than they are. At 15 days you are about 11 percent settled, shaped softened, dropped and fluffed. "Drop and fluff" refers to the fact that as the skin stretches and the muscles relax, the implants move down and out slowly – about 1 percent a day. It’ll be about six weeks before they even begin to settle down, but they’ll be close to 80 percent settled and softened at three months. Watching their progress is like watching your hair grow. You don’t see a difference in your hair growth daily, but all of a sudden you need a haircut. 
Be patient after surgery. Give yourself a few months before making a judgment about your surgical results. You won't know the outcome until then. 
Dr. Ted Eisenberg, Board Certified Plastic Surgeon and Author

Great question. So the implants are very high riding right now. You are fresh post surgery and assuming the implants are under the muscle you need to allow about 3 months for the skin and must to stretch and the implants will drop. I am assuming you have smooth round implants. IF they are textured they will not drop much at all. Once they drop the lower breast poles will appear more round and larger. This is the way almost all look right after surgery for several weeks. Hang in there.