I think the limit is either 1000 or 1024 vertices on a single surface, and a model can contain multiple surfaces.
I wouldn’t use that model, as others have said it’s blatantly not a WW2 plane, and still won’t be even if you change the texture. Over 4000 polygons is stupidly overdetailed for an object like that anyway, it should be possible to get a plane that would be decent looking by ET standards out of well under 1000. Generally ‘free’ models will have been built with rendering in mind, and are likely to be poorly optimised* and unsuitable for game use.
Surely someone must have made some more suitable plane models or prefabs you can use?
(* By game model standards, they’d be fine for rendering)