A properly installed spacer should not yield any driving adjustments on the street. I have driven multiple stock G80's with and without my 15mm set up. There are no differences with this or the 30 plus other cars Ive used spacers on. The contact patch of the tires remains the same so anomalies are probably attributed to a bad install or a bad spacer which is not hubcentric or not placed correctly on the hub.
Here is my other G80 with 15mm square setup:
