Thanks for all your advises.
I decided to add photo outside the window, but it made my render look really dark, so I've changed the setting of the camera to:
F-numer 8
Film speed 320
Shutter speed 30

There are some new stuff on the model, but in general it is the same model as in the first post.

@rspierenburg:
Firstly I don't take your advises personally, they were really helpful 😄

I've change all the whites and used different shades for wall panels, furniture and paint. You were right, it looks so much better Downloaded and used in the model, although I don't see much difference. Maybe my settings are incorrect? I've added some bumps etc. Changed to 65

@tparks
It is on. Amount 0.6 Subdivs 12 Radius 30 - although I'm not sure if is it optimal.

Render looks so much better now, but the shutters are overexposed. Environment is 1,0 for GI. Or maybe the fault is somewhere else?

12.jpg