Normally the fine details would be some through something like a normalmap, which gives them the impression of being 3D when they are actually 2D. They also have access to stuff like shaders worth a damn, so you can make a hexagonal or even cubic model look perfectly round (if you look closely at the ends you'll usually be able to see this) by fiddling with the normals. TMT won't support anything remotely like this so we just have to get by. Even if it did support them it's unlikely it would have much of an impact on the rendering cost.
tl:dr learn to make models efficiently. You'd be surprised but you can usually cut the part count down by a hell of a lot while maintaining the detail. I think I could say something about having your cake and eating it but it's yet to come to me.
olmocapWOT wrote: Is there a way to make the models less laggy chainging the mod code?
If it reached the half of memory using by part it would allow to make much better models
Not really. This is just down to trying to render a shitload of polys (typically considered bad practise in the industry). We can optimise stuff by putting it in render lists (which TMT does automatically) but the reality is we're always rendering a bunch of pointless polys, which bumps up the rendering load and makes it lag.
Only thing that could maybe reduce it is implementing something like occlusion culling. Last guy I know who tried to do that in MC went mad.