A few years ago, our resident tire expert, wmtire, reminded me that the inch size of the tire (14 inch, 15 inch, etc) refers to the size of the hole in the middle of the tire. If you go from a 14" tire to a 15" tire, the new tire has a bigger hole, and therefore requires a bigger wheel to fill it.
Mecicon, some '08 models are lifted, but not with a lift kit. TM moved to an axle with a higher rest angle in order to avoid the expense of a lift kit. So model year doesn't guarantee to answer the question - and looking under the trailer to see if there is a lift tube doesn't, either. The "three inch measurement" is really the way to tell.
And Naturegal, most of your questions have been answered in one of the long threads about changing from 14" tires to 15" tires. I think you will get more info, and quicker, if you read through those threads. Here is one, but there are several with similarly descriptive titles.
http://www.trailmanorowners.com/foru...ead.php?t=6245
One more thing. When you get new tires and wheels, the wheels may come with rubber valve stems installed. These are not adequate! You should require that your dealer replace them with metal stems. Expect to pay a couple bucks more per wheel, but that is no big deal. Again, there is lots of info on this topic in the Tires forum.
The Search tool is your friend!
Finally, when you buy new wheels, make sure that they are rated for 2200 pounds or so for each wheel. The rating should be stamped on the inside of the wheel - the part that is covered up when you mount the tire on the wheel. There are some cheap 15" wheels out there that are rated for only 1500 pounds, which is a step down from the 1870 pounds on the 14" wheels you now have, and totally inadequate.
Incidentally, the wheels you need are very common trailer wheels, used on many utility trailers as well as on RVs. Your tire dealer probably has them in stock. These are white painted steel that look just like the original TM wheels. You can pay more for a fancier wheel, of course ...
Bill