I think I can offer a reasonable (albeit subjective) comparison. I have just changed from a 2014 A3 sportback with se suspension to an A4 Avant s line with the s line sport suspension. My wife and I do not like hard suspension (hence the se set up on the A3) and we do not notice a great difference between the two rides. My A4 was a stock vehicle, so there was no choice of suspension, but I had test driven an s line and it seemed quite OK to me so I already knew it would be acceptable.
Before the A3 we had an 8P A3 with sport suspension and that was downright uncomfortable on uneven roads, but I think Audi have improved the ride with their sport set-ups considerably. I think you'll find your new A4 compares favourably with your A3.