Thanks everyone - I hadn't considered the XL rating factor. As to tyre pressure, about the same for both sets, somewhere around 30psi front and 29psi rear - there's never more than the 2 of us in the car.
The 195/55R15 tyre size has a higher load index than the much lower sidewalled 185/50R16 tyre size. Hence, you can often use lower tyre pressures with the 195/55R15 tyre size compared to the 185/50R16 tyre size. Up to 4psi lower. As you are only carrying two passengers, try 29psi front and 26psi rear.
As the Audi A2 is such a light car, you may find that you use higher tyre pressures than is needed for the tyres to support the weight of the loaded car. The additional tyre pressure being used to improve the car's handling. For example, with just two passengers and 195/55R15 tyres, you may find that 26psi front and 23psi rear is enough for the tyres to support the weight of the loaded car, but because the tyre pressures are starting to get a bit low you may find that the handling starts to suffer.
Try 29psi front and 26psi rear and let us know how you get on. You may not notice the 1psi drop in the front tyre pressures, but you should easily notice the much larger 3psi drop in the rear tyre pressures.
After that, you may want to compare 26psi front and 23psi rear tyre pressures. You should notice a big improvement in ride comfort, but at the expense of worse handling. Tyre pressure helps to keep the tyre in shape when cornering, so you might notice that your handling isn't quite as good after a 3psi drop in tyre pressures, but the upside is improved comfort.
Probably best to stick to 29psi front and 26psi rear with the 195/55R15 tyres, and if you want more comfort in the future consider a more comfortable tyre size. 165/65R15 on 5Jx15 ET28 rims is something I would consider. Compared to the pepperpots 6Jx15 ET38 rims, 5Jx15 ET28 rims will increase the front and rear track by 20mm.
Vredestein Quatrac 5 165/65R15 81T (Euro Label C C 68dB)
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Michelin Energy Saver 165/65R15 81T (Euro Label B A 68dB)
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There's also plenty of good winter tyres in the 165/65R15 size.