My Dad and I used to fish the Kankakee in a 12' V-hull with a 9.9 on it and never had a problem going upstream, at times we would even be loaded down with camping gear and firewood...during low water there was an occasion or two that I would have to get out and drag the boat. Depending on where you are going to launch from,(we used to launch from the public launch down river from the state park, on the south side of the river. There is a number to it, I'm sure Norm could provide it in one creek of the knee) the Kankakee has a pretty decent channel that if you stay in the channel you shouldn't have any problems with a 15' jonn boat. It should only take a trip or two and a decent depth finder to learn where the channel is, go slow to save the prop until you get a good idea of where you need to be. From the recent pictures I've seen on here it looks like visibility is pretty good on the Kank and that should help if you have a spotter up front to help guide your way.
I would say the Dupe is a no go with a boat of that size, but it would also work well on the Fox.
If your ever looking for a partner, I would love to fish the K3 from a boat again and would be more than willing to show you a few spots.
Tim