Have you looked here, at offsets against rim widths?
http://felgenkatalog.auto-treff.com/
You can then do a bit of math for each wheel and see where it fits in the F10/F11 working envelope. You don't say what rim widths you have, but I see the F10/11 351 (8.5" x 19", ET33) having a bigger offset, so your 172 (8.5" x 19", ET18 ?) will already be further out by 15mm, without spacers.
I assume you are changing tyres to get the F11 rolling circumference, (RC) as the E61 is down a size on the aspect ratio, compared to the F11.
HighlandPete
PS: I think I'm reading you wrong... you have the 172 wheels, and/or you want to space the F11 wheels by up to 15mm? Not sure what clearance you'll have, I'd look at the largest sizes available as OEM, and see where the outside dimension comes.
Pete