in your case using exit portals would speed up rendering a lot!
Another approach to get rid of noise that I like to use a lot is to render in 200% of final size and then do some light noise reduction and resize down to 100%. By this you keep all details, but get rid of more noise then rendering in 100% for the same time!
Another "issue" in your image is the DOF blur. Your scene don't seem to need some, but area in the front is blurry! DOF blurred parts need more samples to clear, so take care to export your scene in real Life measurements and check the cam to get rid of the Blur.
Last point is the "NoNo" to use pure white color, that slows rendering down a lot since light bounced in the room for ever. 80% white (204RGB) should be enough, and getting your walls white is in the end a tonemapping thing
