This will work with every A15 ROM?

This tutorial is basically universal with every Android 15 ROM (YAAP, RisingOS and InfinityX.) InfinityX will require you to flash its boot.img file. Rest of it is just the same.

Any Android 16 ROMS?

Not at the moment, even at its beta state. There have been no known Android 16 ROMs, or at least nobody built it yet. GSI's also won't work, even in a Custom ROM. I don't know how the install process is gonna look like, but it was confirmed by someone on the Realme8 AOSP Telegram group that a Android 16 rom will be in the works (when it releases)