[spekoun]

Hi mesh. I was trying to render perfect daytime pic too. And I got similar noisy results. First ensure you have not glass in windows. It brings much of noice.
Anyway. Now my opinion is. Your picture is good. Light distributioin is correct. But we always want to get what we see, but we would expect what we would take with camera!! (complicated sentence, hope you understand my english). And when scene seems dark just increase f-stop or shutter speed. Camera can do this automacally in reality. Or if you have little light in room just use a flash like in real too. And of course. Be patient. 5 hours is very few for maxwell on single CPU.
That is what i noticed with Maxwell yet.
Here is my result:

You can see. Deep room with one window is simply dark. Real camera will turn on flash automatically... Of course noice... I was elaborating light, so i did not wait..
And night with flashlight only (9hour rentime, sl 16) less noice in shorter time:

[smooth]

spekoun, where you using glass on windows in that daytime shot of ur interior ? also, how did you manage to get the background to whitish and bright ? did you raised up shutterspeed or what ?