16" rims will absolutely fit...no matter what, with no exceptions....and depending on the brakes, the 15's might too.

As for the wheel width...they're wrong...I'm running 305/70/16's on the stock 16x7 rims...for 100K, no problem....and there's plenty of others running 33x12.5's on the stock 7" rims as well...all w/o a problem.

For street tires, where you don't want a bulge, and you want the edge of the sidewall even with the edge of the rim, sure, they're OK there...but as far as truck tires go...you can run 16x7's with 12.5" section width tires.

So - the 33x12.5's are a bit cheaper in a 15" size...I recommend trying some on for size, and see the clearance, there's a GOOD chance it will be OK...some people have clearanced the 15's to fit...but I forget what year they had to do that for...round headlights, but after that, it got hazy...

Hope that helps!