Right now, we are trying to calculate how much time we can gain on "preparing" a scene to render using brute force GI. So no ambient occlusion and direct light hack, no photons, etc. Ideally it should have a fast setup... usually given by brute force GI or pathtracers.
The first image which is cleaner I got from blender's Cycles, but it took 4 hours on GPU.

This is the best I could achieve with Clarisse, I left it render over night.

Can anyone give me advice on getting a cleaner render? Ideally in this challenge we were supposed to use only an dome/environment white light or a white emitting sphere, but in these two images I had to use area lights in each windows to reduce the noise. Issues with normals, faceting, etc. on the file are neglectable, we are only interested in the GI solution in this case
By the way, the cleanest/fastest image we have right now in the challenge came from Houdini. Around 24 minutes render time on my machine.
Thank you.
Andz