How is its performance
Yeah 15psi may be a bit low for the A4. Thats around what the Minis and Clios use when on A048s but obviously they are a decent chunk lighter and a higher performance tyre. Jock the Dog on SRS may have the pressures he uses on his S4 at knockhill available.
My friend who used to race the Minis and has a Clio Cup for fun now runs them at that and I was surprised how low we started out. We were lapping around the 1:40 mark in amongst the other cars. Brakes were the thing holding him back after 5 laps. He had Ferodo 5.1 Fluid with DS2500 pads and the pedal was going a bit soft. We bled them a few times but I think the fluid was the issue and Motul dot 4 660 stuff is better.
You could maybe fit a cupra splitter and feed it to the undertray from the centre of the splitter ?