Confirmed; just tested on my machine (Firefox, i7-3632QM @ 2.2GHz) by mashing on the keyboard. CPU spikes to 100% on one core and results in stalling.

In contrast the React+Redux app I'm working on uses the local Controller/Component state method and mashing on the keyboard there gave ~20% CPU.

I never would have imagined that Redux Form would lag on a desktop/laptop. I was more concerned that mobile performance would suffer. It's kind of impressive that a simple form can lag a desktop browser...