A couple of similarities with here in the UK
One chap here wanted a track laying vehicle license and took the test in his Universal (Bren) Carrier - I'd have loved to see that. My Sno-Cat steers by articulation rather than track braking, so you could argue that I wouldn't need that license, but since it has all-steel tracks chances of me wanting to drive it on the road are really slim.
The UK is now pretty much lined up with Europe about license limits, so an ordinary car license entitles you to drive anything up to 7500Kg, which has to be the same as your 15,000lb limit. Trouble is that it is GROSS, not NET, so if you are driving something at 7501 Kg it is an offence. When I had the DUKW I just drove it anyway, although it was 2" over width, and would you believe no-one ever stopped me? or if they did they are tucked up underneath the hull somewhere 'cause I didn't notice them.