Hi Shift, glad you like it! :smile:
Wow your Mac is fast, my MacBook needs 39272 s.
The Problem with those PBR materials is that they have reflection always activated (specular value = 0.5 default), even on diffuse surfaces.
That means that refractive caustics come into play and slow things down.
Deactivating caustics would mean loss of light and defy the PBR concept.
For diffuse materials (in PBR that's roughness close to 1) you can set the specular value to 0, making it a diffuse shader producing no caustics.
That's what I did to the wall material in the last file and it immediately helped, but of course the subtle reflectance of the wood materials is essential and has to stay. A material shader with blurred reflection would cause the same problems.
Indeed I think after countless tests that adaptive sampling currently doesn't deal well with the caustic noise (for diffuse only it's ok) and needs better detection and/or adjustability.
Also this is the reason why I'm rooting for a denoise function, in Cycles this scene would probably be done in an hour on CPU and with GPU support you could animate it.