The principle of adaptability render Biased engine to which, for example, a V-Ray, lies precisely in the fact that in well-defined, ie bright areas, rendering quality more accurately than in a poorly visible in the rendering, that is, the dark areas of a scene. As a result, the darker the site, the more noise there.
It should also be understood that all areas where not exposed to the direct rays from the light source may be illuminated only by GI, that is re-reflected rays from the surrounding geometry, initially emitted from the light source itself. Of course, re-rendering the reflected beams is more complex than straight. Therefore, the noise from the "secondary housing" more than from direct sampling.
With specific regard to your case, then you have a very low quality render settings . Here no options, only to increase rendering quality, as well as the right to install light in the window 😉
Render Settings will not comment, they differ from our recommended.
As for the lights, then you are not truly understood. Look carefully at the diagram position lights o from my previous post. They are not outside, but on the contrary, they are in front of the interior curtains inside😉