hello rawa
as you can see in the LAST picture in this thread I change nothing except parameters which you instruct me - production defaults, solvers. I realy like Corona because it produce nice pictures easy without hours of tweaking, tunning and lots of test renders.
You should change a few things in this scenario to get even better boost. You should use generally HD cache as secondary GI only in cases where light has a bit more complex paths, like interiors, where light has to enter a room through an opening, or reach some deep place in general. You should think of environment like a directional light (inverse sphere).
So in case of lighting by HDRI, like in your food scene, and pretty much any scene, where majority of the surface captured on picture is not occluded from direct reach of environment lighting, you are a lot better of be setting secondary GI to path tracing too, as that will make rendering in this case a bit more efficient ;)
In those cases, you can also afford to lower PT samples from 16 to 8, eventually even 4 if you use DoF. The lower PT samples value, the more samples are devoted to rendering of DoF.
I can see that you already switched secondary GI to PT. That's good... so i hope this helps you to determine when to use PT and when to use HD cache as secondary GI ;)
