Animation - UHD Preset

I’m attempting an animated interior with Corona.

I noticed that when I have my UHD preset to ‘Still frame’ the precomp is pretty fast (23seconds - good) and the render time is OK, approx 5 mins.

However, when I set the UHD preset to Animation (as I was getting unwanted flickering) the precomp goes up much higher (as expected) but the render time more than doubles to 12 minutes.

Why? My understanding is that only the pre-comp should go higher…Or am I mistaken?

With the animation preset, the UHD Cache is more precise, which also means that Path Tracing will be used more. More precise rendering = slower rendering.
If there are no moving objects in your scene, or if the movement is very subtle, maybe you can compute the cache once and re-use it, or use the load+append option?
Here is the UHD Cache guide: https://coronarenderer.freshdesk.com/support/solutions/articles/5000515648