Use light cache for glossy rays is great way to reduce render time, but sometimes we have artefacts with it.

There is simple way to avoid it, it is to turn Off prefilter and On Filter Fixed in Light Cache Reconstruction_parameters with value if Filter Size 2-3 times bigger then Samples Size of Light cache.

For quick Exterior preview rendering, you need to put Vray Light in a mode Dome Area Light type and put in to Texture Sky (image, hdr or shader). Other settings are not necessarily touch. In this case, no need to include the GI, and you can see quite quickly lighting and materials. This is how it will turn out, and render final. But! Will be noisy and not very fast. And most importantly - too deep shadows. Making a contrasting picture easily. We should only reduce the gamma in color mapping.