Bike Shoes Size 15

Gear and Training carries a lot of Sidi in size 50. That's where I got mine.

http://www.gearandtraining.com/gearntrain/dept.asp?s_id=0&dept_id=10320

Your best bet is to go to your LBS and talk to the owner/manager.  Find out what brands they carry that make bike shoes in a size 15(not many do) and get them to special order them for you.  You may pay alittle more for the shoe but you will most likely save on shipping and that should come close to evening things out.  This strategy does have a few big advantages.  If something goes wrong with your shoes the LBS will have better customer service than any web store does.  Additionally it will start a relationship with you and the store.  People dont come in everyday looking for size 15 shoes, the owner/manager will remember you.  If you continue to shop there you will be treated right and you will likely be able to negotiate a better price on big ticket items when you end up buying them.