V16 plugins keep backwards compatibility is intact, however note that there is a new optimized storage system using a new format.
- If you save projects with the new version, old versions won't be able to read the settings.
- If you'd need to downgrade for any reason, first go to "Settings / Compatibility settings" and enable "Storage compatibility mode for V15", then save the settings.
- Also note that V16 no longer provides 32-bit plugins on Windows. You should be able to run V15 32-bit along with V16 though. Simply do not uninstall V15 and do not perform plugin cleanup.