It is the overall diameter and width of the wheel/tire combo that determines whether or not the thing fits in the spare tire tray under the front of the van. The offset (or the ET) of the wheel should make no difference.  Does your current Audi 15" setup fit in the spare tray?  If so, then if you get a different 15" wheel and use the same size tire on it but the new wheel has a different ET (stock is about ET30 and your Audi wheels might be ET45 if you require spacers) that should make no difference.  
There has been plenty of discussion over the years of the largest sizes that will fit in the spare tray; both the fit in an unmodified tray and what will fit with which modifications to the tray, but offset should not be a consideration.  I'm sure someone will correct me if I'm wrong but I don't see a problem.  Good luck!
Stephen 

    On Saturday, January 7, 2017 11:48 PM, "Lacy, Reed H" <reed.lacy@HP.COM> wrote:
 

 A friend with an 86 Westy posed this question to me that I couldn't help with, but I'm hoping someone on this list can:  Here is her situation/question:

Currently my wheels are 15 inch (older Audi wheels) that require spacers to accomplish the proper offset/clear the body of the van. My main goal is to get wheels that can be mounted without spacers, as many mechanics (bigger chains such as Les Schwab, Firestone, etc) won't work on the van once they find there are spacers there.  Also, there is a safety issue (depending on with whom you speak).  I know I can purchase new wheels that don't need the spacers, but there is the strong possibility that the spare will no longer fit underneath the vehicle.  Any thoughts or suggestions on this?

Thanks for any shared wisdom in this space... Reed