On an M12 X 1.5 thread, it needs 15mm of thread engagement to achieve maximum clamping load capacity. You'll find that with spacers, you probably have about 12mm of thread engagement, which isn't really enough.
I had 5mm spacers for the same issue but wasn't happy with them and replaced the rims.
With the way tyre fitters and mechanics hammer in the wheel nuts you need every mm of thread to keep you and your family safe.
The other issue with spacers is...