I remember reading on lost jeeps someone was using 15" cast/alloys on theirs, but I didn't ask about it to know more, and there were no pictures.
I've seen success with 15" steels, so the fitment for cast seems right in the gray area, a try it before you buy it kind of fitment it seems.
I think it was one of tom's posts I read where some wheels no longer fit well with fresh brake pads in them, which I didn't think about before researching.
I'm currently using spacers as mine had dry rotted tires on it when I bought it, I needed something extremely budget and 16" steels with tires from newer wranglers can be found dirt cheap. I held out for and recently found some 16" american racing wheels off a tj that I can put on after I lift it. I had no problems with my spacers over the last year on this vehicle towing a few times a week or on tj's in the past, but for me it will be nice to have 20 less lugnuts to worry about, and no more cleaning the loctite off the threads every time I work on it.