195/60R15 is a 4% larger circumference, so speedo will under-read. 195/55 will be ok, but I fail to see the advantage over a 185/60.
Opinion: 185/60R15 is a very good compromise between comfort and lack of roll. I have these as winters, I'm now on the second set. I disagree with 185/65R15, they are too big.
Quick Price check: Conti premium contact 6. 195/55R15 = €116. 185/60R15 = 101. 185/55R15 = 99.
opinion: Replace all four, go 185/60R15, shop around. Should be able to get Hankooks below €80 / corner and efficient grips at €100; Primacys seem to be at €111. The BluEarths on the A2 are quite quiet but only c/c.
Regarding the back slipping out: I say no, it won't. Car and ESP both say "no". Offspring recently took the A2 to the summer house (I was quarantined) and it appears she decided to take a (shallow) left turn at about 70-80km/h "oh no, i need to go to the store in that little town and that was my turn <pulls steering wheel>". Tyres squeal and car slides, no ESP. It went around the corner, she was a little shocked but no harm, no foul. Glad she didn't try it in the wife's car...
The back end does not kick out and believe me, I have tried very, very hard to get it to. I've turned off ESP, I have the rear ARB and it just won't go, I have tried with space, ice, snow and gravel. Gravel is the only one where I've got even close, and even then there's just the start of a slide, not the rear trying to overtake.
The (4x4) Superb and (4x4) S-Cross will both powerslide nicely with ESP off, destabilization a.k.a a scandinavian flick, and some power, but the A2 resolutely refuses to do it. Phoenix / Andre did some testing with dishes under the rear wheels of his A2 at the last ice track and he was disappointed. Even with spikes on the front and friction tyres on the back, Thomas still couldn't get the rear to kick out, also with ESP off. I didn't try this on wet ice, I can put this on the list of things to do at IT23.
Straight line stability on crappy (read: gravel)
or wet surfaces is more the problem, especially when braking. I might see if I can get Offspring to take the car to the summer house again and then drop an action cam onto the spoiler when we brake from 80km/h on gravel, just so you can see the tail wag. You could absolutely feel it in the 307, it's incredibly unnerving. You already have a significant proportion of the weight at the front and braking forces that even more.
This is also why you really should go and attend some road safety days, in your own car, so you have a clue what to do *before* it's brown trousers time. When the cruise clicked off in the Superb while overtaking a truck on a snowy hill, I knew what was going on and why; when trying to slide the s-cross, I'm aware of how much the right foot controls the slide versus the tyres and just how much opposite lock is needed (just a dab, honestly)... and just how fast I end up going because I've applied power through the slide. Practice helps enormously to understand.
but if the rears aren't up to it then the back comes out 
