Thanks for all the comments ! 
Yep, the pavillion scene is directly inspired by Roman’s “the third and the seventh” (and yes it’s a part of Pavelló Mies van der Rohe in Barcelona^^).
(“the third and the seventh” … I watched video like a million time 
It’s so amazing).
“16 for the spots? So you are NOT using inverse square falloff?”
Oops forgot to mention that ! I’m not using inverse square fallof for the spots (and the light fallof is set to 0.0001).
*Also…with exposure settings like , dont you have to almost kill the bloom completely as well? *
I set it at 0.25 (or 0.5 for the stairs scene).
how do you setup your reflection capture actors?
Well, the simplest possible way
For the “Blue chairs” scene there is only one BoxReflectionCapture that cover the entire room and for the “Stairs” scene one Box for the room and one small sphere (for better reflection on the chairs). But most of the reflection is done by the screen space reflection (intensity 100, quality 100 and I use the command r.SSR.Quality 4 to have the best quality).
You can calculate Lightmass in under 10 min with these crazy ini boosts AND bounces set to 100 …
If I remember well, around 10min without the sun and a little more with.
Added a lots of secondary bounces don’t add significatively more render time.
are you using the skylight in the new pavillion scene?
Yep ! And a big spot/reflector to add a little directionality in the ambient lighting.