I took a few pokes at it...and the diagnosis isn't too good...
The model itself is most likely the culprit. While I didn't notice any real slow down on my main machine, when I loaded it on a test box it didn't really car for the model too much. Running with no scripts at all, the model caused lag as it rendered on screen.
There are a number of resons for this.
1) You have two skins assigned to it. Although they both look identical, the engine is flipping between the two, and it is taking more texture memory.
2) The skin is 1024 x 1024. Is this really needed? Try using a 512 x 512 skin. Its only a quarter of the size in memory so it will load much faster.
3) Lots of time spent on unseen geometry. The mesh itself, while detailed is gluttonous. You have a lot of polys that could be stripped out and still have the sameammount of detail. I am guessing you could probably cut the polygon count in half without loosing much detail.
4) If you want to keep with points 1, 2 and 3...upgrade your video card. From the few tests I ran I would guess your video card is either an nVidia Geforce2 or an ATI 8500ish card. On my new cards it ran with almost no noticeable delay, but on those cards I did get the stated hesitations.
Hope this helps.