Sir Sam wrote:
its very unlikely that 15" will fit, only a few do.
Also, these days there are better selections for 16" tires. Why? Because more vehicles have 16" tires.
I remember 10 years ago when one of my XJ's had 16" wheels, and the other had 15". I was somewhat annoyed with the 16" wheels because I had fewer choices and they cost more, these days the inverse is true.
For example, for a 30x9.50x15 from tirerack, there are 17 tire options.
For a 245/75/16 (a slightly bigger tire) there are 85 results from tirerack.
For a 245/70/16 (a slightly smaller tire) there are 46 results from tirerack.
So I think its fair to say there are more options these days for 16" tires, and its likely only to increase as more and more cars come with larger tires.
But you also got to look at those sizes and what rating the tires are.Most(if not all) 245/75R16's are "E" rated tires,most(if not all) 245/70R16's are "P" rated tires.When you drop down to 15" rims you can get a good tire in a "C" range.
Oh and without having to run spacers and big lift(to turn) there is only a handful of aftermarket steel rims that fit a KJ,no alloy 15" will without spacers.