There are some informations from the underground that soon there might be a new version of Corona with greatly improved direct sampling, just a rumor... ;)
LSM set to 16 is an overkill. You are casting 32*16=512 direct light samples / pixel / pass! Using a lot more direct than GI samples may be required, but then you should probably decrease GI samples. So you can for example try GIvsAA@4 and leave LSM@16. This way the ratio between GI and direct quality should remain the same, but you will get a lot better per pass performance and much more pixels will be sampled.
Another idea is to use buckets here as there are some large flat solid areas in your render.
Do you have portals in your windows? You could also try placing one in that "hole" through which the noisy top-right corner light is shining. Not sure if this will help, though.
It sits inside a "thin" clear box.
If there is a light inside a reflective/refractive tube, then this could be casting some reflective/refractive caustics. You could disable them by nesting the glass material inside a rayswitch material and clearing the GI slot to make it completely invisible to lights (it will also stop casting any kind of shadows).
