That's easy. Cut it into the normal eighths and then split all but one piece in half. Your bad project specification didn't say all 15 had to be the same size. :-)
Maybe pizza restaurants should be like the one on Breaking Bad which doesn't cut the pizza and passes the savings on to you. One of the commentaries said the writers added that after people complained about a scene where Walt threw a pizza onto his roof in a fit of anger and it hadn't been cut.
“Easy enough calculation for us engineers, but it was always a treat to watch the arts students who worked at the pizza place try to work out how to slice a pizza into, say, 15 pieces.”
“That’s easy. Cut it into the normal eighths and then split all but one piece in half. Your bad project specification didn’t say all 15 had to be the same size. :-)”
A couple months ago, I requested that Pizza Hut cut our large pizza into twelve slices instead of their usual eight. When we got our pizza, it was indeed cut into twelve slices, but eight of them were half the size of the other four.