Thank you mr wilks, my guess is 25 mm rear. You may ask why - those wheels above looks like style 224 without spacer on non-m zed.
Then 8,5 ET 50 minus 9,0 ET 30 = 26,4 mm more towards outside the vehicle = 25 mm. Just from observation.
Do you think 15 mm is safe on front on 8,0 wheel ET 47? Car is lowered.
BTW Did you really had like 15 zeds?