I am looking at this kind of like shouldazagged does. While I really don't care what the wheels/tires look like on a utility trailer I would hate to further beat up something that could be important to someone else. I think maybe I'll just take the old tires off the wheels and see how much work it would be to strip them down and see what is left of them. The wood actually looks very solid. My curiosity has been peaked and I would still like to know what they were off of. Maybe I just have to much time on my hands.
I think this is the best plan of action. There is also the safety factor. While the wood looks good on the outside, you don't know how good the center and the attachment points are. 15" rims and tires are cheap at the junkyard.