Here is the same test with Corona 6.
Ok, noise level difference is about the same as with Corona 7. But now I'm confused by the overall render time with the same noise limit
Corona 7 - 2.44
Corona 6 - 1.46
Materials which I've changed to render these pictures with Corona 6 are wall material and sofa fabric (they were new physical mats). Wall material was simple, no maps, only roughness was adjusted. Fabric physical mat - pretty simple, had Sheen effect adjusted. And that is it.