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In this scene, I see 2 things that will cause lots of noise and artifacts: bad noise treshold settings and difficult light sources.
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Bad noise treshold settings: In a dark, interior scene, you will want to manually set a number for the min samples, because you are going to need a lot of them. The min samples is the number of samples Cycles will do before it starts to use the noise treshold. When the treshold kicks in, Cycles will stop sampling any area it judges to be low on noise (based on the treshold number you choose). However, in a complex scene, this can cause a problem where Cycles completely misses sections of reflections, because they haven’t had the chance to appear yet and Cycles mistakenly thinks the area is done and leaves gaps in complex reflections. When you leave the min samples at 0, Blender will pick a value for you, which might be too low in a difficult scene. Try manually setting the number at 128, and if that’s not enough, 256.
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Difficult light sources: mesh lights are noisier and harder to sample than light objects. If your ceiling lights are just emissive squares, you could replace them with area lights (which you can make visible to the camera in their object visibility settings) and you will likely get less noise. Also, light coming through a mostly closed door is a famously difficult case to render for any path tracing renderer. You might want to try using path guiding. Its available only for the CPU at this time, but in a difficult case like this, it could be worth the performance hit (though you will have to try to know for sure).