Even the standard size 195/65 R 15 already looks very good on the Audi 100. About the dynamic properties: 195 tires are more than sufficient - also with powerful engines. Advantage: narrower tires (compared to wide ones) have less resistance during running-in and reduced running noise with the same profile.
Tires in size 205/65 R 15 compared to 195 tires - the service life of the more expensive tires is only slightly longer, and the dynamic properties are almost the same. Conversion is only interesting for those who like the appearance of wide tires.
205 tires can be mounted on the same rims as 195 tires, so when re-equipping, it is not necessary to buy new rims.
With 215 tires, things are different: they can only be mounted on 17J-15 rims
Winter tires
If your car has standard size 195/65 R 15 tyres, then, depending on where you drive it, you can probably drive in winter with summer tyres, provided that the tread depth is sufficient.
As for the wide 205/65 R 15 tires, the situation is worse, especially on models with more powerful engines. These tires are prone - not least due to the "harder" HR brand - to early slippage on snow and ice. In this case, it is hardly possible to do without buying special winter tires.
When buying winter tires, you can choose between regular M+S tires that can only go 160 km/h, and expensive high-speed tires for fast driving at 190 km/h.
In vehicles that can travel faster than the specified maximum speed of the winter tire (see beginning of chapter), there should be a plate on the dashboard indicating the maximum speed of the tires. The maximum speed of your vehicle is stated on your registration certificate.
An M+S tyre with a profile depth of less than 4 mm is useless in winter. If, for example, winter tyres are prescribed in the mountains, M+S tyres are only considered as such if their profile is at least 4 mm.