Not to mention it would make SE's development/release schedule unnecessarily complicated. If they were to rename it then having it ready before XV would be a problem. They'd have to delay it until after XV's release, even if there comes a more optimal time to release it in the meanwhile. And I'd imagine they'd want to place a good chunk of time between the release of Type-0 (or, in this hypothetical case, XVI) and XV, since both games cater towards largely the same audience. Don't want that customer overlap!