I think this truck has lots of triangles that can be deleted. Can you post the tricount? Also 2048x2048 is a bit high for a lowpoly texture, switch down to 512*512 and it will do!
Are you sure? Trust me, you can have as much N-gons as you want, but the performance is always the same, because the 3D software (or the game engine) counts triangles and quads, but not polygons. ;) A 2048*2048 texture will significantly lower the performance... Mine was a suggest, but I repeat, I think that you may better…