No, no you've got it right with the spacers. Offset of 40 and 25mm spacers make it ET15, but I would try to avoid spacers as much as possible. First because they are expensive, second because essentric spacers are very expensive (*the lip the wheel rest on) and third because I've heard people managed to snap them off at drift days. Oh and actually I forgot a 4th disadvantage and that is having to buy longer wheel nuts.
This is why I like deep dish wheels, they look fantastico and the low offset saves you money on spacers. If they could make lightweight deep dish then it would be better but doubtfully cheap. I avoid BBS because of pricing.
On the other hand you are in Holland? Try to check what Kerscher, Borbet, or my favorite brand Brock are like on the german ebay.
Here is one running on Kerscher