Well, I use both Vray3 and Corona (80perc. of time Corona only though). In both, on average i7 (I have farm though, so just for relevance) my pictures do take 10+ hours to render :- ).
With Vray you can optimalize a lot, cut paths to 4-6 bounces, Heavily biased cache (-3/-2 or -3/-1 Irradiance, thus solving GI only in 1/4 or 1/8 of final image resolution both in interpolated quality),
something that's not currently possible within Corona.
But once you compare similar visual quality (BF/LC) you will see a quite decent speedup, one that's even more noticeable in heavy GI scenes lit with IBL, where Corona is quite much faster.
But if you compare default Corona, to whatever potato setup you had, it will be slow I guess. This is the problem with people claiming Corona to be super fast, it's not. For some it's fast, for some it's slow...