I've been working on a way to use only vraysun &sky for interior scenes, cause with that render times get really short... Perhaps I'm not doing the right things, but here are the conclusions I got...
I found some problems on that...for instance if you have a room with a little window, you'll get all burned near the window (even with exponential colour mapping) and in the other side of the room there is no light.
But if you have a smooth floor surface in white or soft grey diffuse, you can set the Generate GI value to 2 or 3 and there you have more light without increasing a lot render times. This won't work if you have a wood floor cause everything becomes brown..
Other problem is that if you see some objects in the exterior, to have a nice lightning inside, outside everything will be burning...so in that cases I reduce the Receive GI value to 0,5 or even 0,2 in the outside objects...
Here is attached a scene playing only with vraysun, vraysky, Receive GI value, Generate GI Value and colour mapping.
King Regards