I am not sure if those elements aren't tied to denoising (so invisible to user).
Anyway, even without those "elements", that would be damn 20GB for 40k polies.. so something is very wrong, even though Corona is super hungry renderer.
Btw, does it throw this message if you restart 3dsMax and hit render first time ? There is big issue with Corona where it won't flush all the data from subsequent renders, issue that's apparently tied to 3dsMax but one that we have to live with for now.
You can try exporting the scene to Corona Standalone to see the actual 'cost' of scene without all the 3dsMax garbage.
Nonetheless hopefully this can be solved in future as other renderers found some way to flush this data.