Jochen. I have sent you an email. Let me know if you don't receive it.
Attached to this post is a pdf file giving tyre size comparisons.
Note that it refers to the proposed fitting of a 195/65 R15 to a Plus 4 but it also includes the tyre sizes Jochen is referring to. Note also that the fitting of a 205/65 R15 would allow you to use a 4/4 wheel with a 165/80 R15 tyre as a "space saver" spare. If you have a spare you need to check that the tyre will fit the space as the diameter is increased by aprox. 2 cm.