[MyF15+F85]

I deal with those problems almost every day, your case s yet another case...
First thing that you must check is the actual fitment of the spacers, it may sound silly but .... are they truly hubcentric ? 99% of the time the spacers are NOT fitting the hub perfectly snug which in return corresponds to a wheel which is mounted off center, and that will slowly kill your bearings, shocks and all of the suspension components.
Second thing that I see a lot of, is the spacer ( especially used one ) that is not cleaned properly before mounting it, anything that is attached ( dirt, rust, greese ) to the contact area of the spacer to hub and spacer to rims ( wheel ) WILL amount to what I call an ERROR which is an assembly out of round. That by default will shake da be'jesus out of ya ! Use common sense when assembling your wheels.
Thirdly, I have seen cheap ( not inexpensive I meant to write cheap ) lug bolts that are not machined properly and will not center or torque properly to the hub, I would amount the least amount of shaking to that , but .... nevertheless it is a problem since uneven torque could result in vibrations, and ultimately crack or warp the rim.
Fourth thing that could produce issues is the actual offset, bu pushing the wheels out even by a 12 mm you will change the geometry of your car and the alignment of your car will be affected, on older cars ( with looser suspension components ) could result in vibrations.
Hopefully that will shine some light in your case and help you some what.

Hopefully that will put you on the right track in finding your specific vibration problem.