Well, if you look at the scores of the games, Wisconsin was never really challenged until the B10 CCG. They were demolishing teams, just controlling the games they played from start to finish. Iowa had a lot of close games in 2015 and had some luck along the way. Plus, look at their offensive and defensive numbers compared to Iowa's in 2015. UW 2017 was better than Iowa 2015.
For example, Iowa beat UW in 2015 10-6 and got a break when UW fumbled inside the five. Iowa had really tough games against Minnesota, UW, Iowa State, Pitt, ILLINI, and Indiana. They also didn't look too good against Purdue after the first quarter, not too hot against a really bad Maryland team, and so-so against Nebraska (good enough, though). They had three easy games Illinois State, N. Texas (just a horrible team), and one truly impressive win against Northwestern.
Meanwhile, UW destroyed Utah State, BYU, Nebraska, Indiana, Maryland, Minnesota, and IOWA. They ground down and pulled away from FL Atlantic, Illinois, Michigan fairly easily. They beat Purdue in game that wasn't as close as score indicated. And they beat NW (#20) in a hard fought but never really contested game. They beat all but two teams by 8 points or more and they beat the other ten teams by 14 points or more. They just beat people up throughout the entire year. They lost to Ohio State by 6 in the CCG with a chance to win late.
I loved the 2015 Iowa team, but this year's Wisconsin team was better. They had a better running game, stellar defense, and most of their games were pretty much over by the start of the fourth quarter. It's not an insult to Iowa; it's just a recognition of reality.