There are several huge differences in the 2015+ F450's vs. F350's. Ford back in 2008 put the Dana110 rear end and 19.5 tires on 2008-2010, but then went back to the Dana80 on 17's through 2014. Why they did this I'll never know, because all they did at that point was to put in 4:30 gears and call it an F450.
The 2015+ F450's have a rear axle rated @14k just on it's own, and the 19.5 tires that can hold it. Dana80 on 17's is rated @10k per Dana's spec.
In addition, since they have larger rims, they also increased the size of the brakes all the way around. I had an F350 and traded up to the F450 and I can tell you the difference in loaded ride feel is tremendous.
That being said, I needed the F450 because of the weight of the camper I haul+trailer tongue weight of 1,000lbs. You won't need an F450 for just a 5'er or 'normal' camper. However, if someday you decide to ditch the 5'er and get a BIG camper, consider the extra few bucks now on an F450.