I have ET13 15x7s on my GTI right now, with 195/50 tyres. Up front ive hammered the metal lip back and chopped the plastic arch, at the back I have done nothing. Car is lowered 40mm, and up front there is no problem, but at the back it scrubs on bumps, and i cant take passengers

Since they have stretched tyres on those you might get away with no archwork at the back, but up front you may as well work the arches as its not hard. At the back its more tricky as they're double skinned!