15", 5.75" wide rim with 3.25" bs

On the RMS site, in the tech section, when looking at the info on the Alterktion, it states for a 15" rim, a 5.75" wide rim with 3.25 back spacing fits with no problem.
Ok, I might be looking in all the wrong places, but I can't find a rim like that anywhere. Also, isn't that a bit narrow?
I have 15 x 7" rims with 4.5" back spacing, P 235/60R15s, mounted on my Charger, that I had planned to use. Are these going to be too larger?
Thanks