You have to play with quality settings (min and max sliders) to tune it for acceptable performance for your scene. Deckard always renders when activated. New version of Deckard has a more responsive mode of rendering in-editor (but it' is still in beta, and is available on a request). Unfortunately, this new version of Deckard doesn't still work with HDRP because HDRP doesn't support custom post processing effects. P. s. I don't suggest using HDRP still. HDRP is full of bugs and non implemented features - and isn't production ready.