Why would you want 15" rims so bad? Seems to me there are more tire options for the 16" wheels, I wanted a set for my old Trackick but couldn't find a set.

That may depend on where you are and also the type of tire you're looking for.

Street tires are fairly common in 16's & up - but for off road tires there seems to be a better selection in 15's - try finding a super swamper to fit a 16" rim.

I am having a similar problem, yes they have lots of 15 inch off road tires, a few 16 inch but the rim price is higher and the tires may be a little higher priced.  I am looking at the 15 inch Crager Soft 8 style and possibly a 30.5 or 235/75, they do look good on the Suzukis/Chevys, plus you have so many choices for tires.  I made the mistake of buying 18 inch wheels and all the tires for 17 inch and 18 inch are 33 inches and up.  I wasted a bunch of money.

Check these out -
http://www.lowrangeoffroad.com/index.php/suzuki/sidekick-tracker-x90/wheels/pro-comp-rock-crawlers/series-98/rock-crawler-series-98-gloss-black-monster-mod-wheel-pcw98-5885.html