I have a set of new 235/75/15 bfg knock offs. I have a 2001 Grand Vitara stock with 16" pretty chrome wheels and bald stock tires. I have a stock pile of stock samurai 15" 5 on 5.5" rims. What's the chances I can make this combo work with maybe wheelspacer? This vehicle is used mainly for street.

It'll work but not a lot of people like wheel spacers around here.

There's a guy on the GV forum here running a similar setup.  I say sell them and find some 225/75R16's or 235/70R16's.