What's the truck they'd be on? 15.5 is a WIDE tire.
If it's mainly a trail truck, I'd get the SXs, if it's mainly road, I'd get the Krawlers. If you already had Boggers, I'd go with the SXs.
I run 38.5 x 14.5 well loved SXs on my Toy, Extreemly happy with them.