hey Lal-O,
there are several issues in this scene you should take care of:
1) your plasterwhite0083_3_ostion MAterial is a texture with RGB values above 204. reduce these in a image editor to max 204 in any colour or reduce it by lowering the B value of the texture (b of 0.85 would reduce the Red in this image of max 241 to 204). Same is for your marble
2) your light emitters are not equaly powered! DoubleCheck your light layers, while layer 1 gets clear quite OK, layer 0 stays super noisy contributing a lot of noise to the whole image. Boost the Emission Sampling Multiplicator of that emitter to match noisyness of Layer 1.
- emission_multi.PNG (5.6 KiB) Viewed 44432 times
3) set your emitters to pure black diffuse, then they'll only emit light and every ray they catch gets killed. this usually boosts rendering performance, depending on Emitter size.
4) disable sun+sky, you still have them active...
5) reduce your Muebles, Plastico blanco, sink, Blanco cristal front and all the others white value down to 204 in RGB
6) make your emitter in the covered ceiling WAY bigger. PT needs to conect this hidden emitter somehow with the camera, the bigger they are, the less noise you get.
7) if not really needed use uniform emitters instead of blackbody, they do render a little faster...
By aplying 1-5 this I could raise the samples/s on my 1080ti from 7,7M to 11M
7) your toilet Doors are made out of glass covering a doublesided thin naterial, thats quite complex stuff that causes some pain... is this intended? changing them to Phong raised my samples/s to 13,5M
8 ) an F-Stop of 2 seems quite high, max it out to 64 to prevent (even subtle) DOF blur and therefore longer rendertimes.
If you use Clamp Contribution then setting it to 1000 does nothing at all... try values of 50 or even 25 to kill unwanted FireFlies.
Give that scene a try on CPU PT+BiDir
....Anyway...if someone wants to give a try to get lower rendering times then just feel free to ask for the model 
