Page refresh between pages is ok. Lag when updating a form based on your inputs isn't. Frontend UI is like a bigger monitor or faster PC - you may not have known what you were missing, but once you've experienced it it's very frustrating to go back to the clunky old thing.
It's really irritating for your users. They might not consciously be able to point it out as the cause of their irritation, but they'll like your app a lot less.
