Assuming everything is in tact and works as designed, then I'd say that $15K is a reasonable price.
Whoa there....
The ME series (I'm not sure where the "B" is from. ME means mid-engine.) Tuckers are a breed apart. The cab configuration is always a two door, two person cab, but unlike every other similar vintage Tucker that have identical front seats, the ME's have a lesser seat for the passenger.
Tucker designed and sold these machines primarily as groomers (more on that momentarily) and they were typically equipped with a six-way blade. The blade could be ordered either with the capability of tilting left-right off the longitudinal axis (useful for cutting a path across a side hill) or with the ability to change the angle of the blade front-back, increasing or decreasing the blade's bite. The blades themselves are made for grooming, which is NOT snowplowing, and are lighter in weight and less robust than a snowplow. This machine looks like it has a pickup truck snowplow on the front which would weigh considerably more than a Tucker factory blade.
While Tucker probably built more two-door cab models than three of four door units, I think recreational snowcat owners prefer being able to carry more than one passenger. Cab conversions are done but they're expensive. But at least with a front engined machine you have that option. With an ME...not so much. I have seen an ME that someone adding an enclosure at the back...creating a mother-in-law like cab setup. If that sounds hokey to you (it does to me) it looked to put it politely, less than optimal. That machine was for sale for a very long time.
Lastly, machines used as groomers tend to get a lot of hours, and hard hours at that. Maintenance and repairs are often delayed and then frequently not performed to a high standard. Yes, some have had idler wheels and track belts replaced, which is a good thing, but my general advice is to avoid Tuckers with a history of groomer usage.
I would need a lot more photos and information to offer an opinion on whether the price is reasonable, and even then an in-person inspection could (would?) reveal things that you can't see in pictures.