if you are going to do spacers, I'd suggest 25mm H&R DRA spacers because these bolt to your hub then your wheel bolts to 5 new holes in this spacer, so no fiddling with a loose spacer.
I've had nothing but problems with spacers that you do not bolt onto your hub first (ie: anything smaller than a 25mm). small wobbles basically, but I KNOW Its not supposed to operate that way, so I remove the 15mm spacers and enjoy a smoother ride and deal with wheels being a BIT inset.

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I swear, my cars are like a girlfriend.
Sometimes its a rough ride, sometimes its smooth motorin'.
Sometimes she doesnt like how i treat her and sometimes i dont like how she behaves.
BUT at the end of the day, she loves it when I am inside her.

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'91 850i
'05 X5 4.4i
'09 Clubman S