Yep it seems 17s are starting to be the smallest you want to go due to tire choice,brake clearance,etc. Now if only the tire companies would stop charging more for less tire
I think the reason they cost more for bigger rim widths is tires are actually harder to manufacture. I remember reading that somewhere.
Another point to consider is if you ever upgrade trucks to a newer vehicle, ie 02+ dodge, you won't be able to use even 16" rims, as 17"s will be the smallest to fit. So if you buy nice tires for the 15's or 16's, you won't be able to swap them to new vehicle. My 10 takes minimum 17" wheels, so when I got it I wasn't able to pull the brand new 16" Hercules Trail Diggers off of my 01 and reuse them.