Indeed, I have 15mm spacers and longer 14mm bolts & studs with
appropriate lugs, on their way.

As far as I know Vanagons use their studs to align/center rims on
hubs; they're not center aligned. But I'm sure the experts on the list
know more than I.

I used to be a machinist and heavy equipment mechanic, so boring out
these holes seems a realistic DIY task to me. Especially for more than
$160 in labor!  Provided I can find a drill press with large enough
spindle clearance to accomodate the 8" or more radius of the 15" rim.