All will depend on how low your car is, ho soft your suspention is, types of road and how you drive on them.
I have heard of people having some rubbing with 15x7 ET40 195/50R15 but that was driving hard on track with low suspention.
If your worried then just use 195/50R15 tyres and dont lower you car to much.
Im in this boat at the moment deciding on 15x7 ET35 or ET40. Heard most people with ET35 have had to roll there arched out to stop rubbing when lowered. Personaly im going for the ET40 to be on the safe side. If its on std suspenssion you wont have any worries at all.