yea I already cut it, but I wanted to know why to avoid it in the future. I'll try shade smooth, thank you so so muchIf a vertex needs multiple properties (eg. because there are faces connected to it with different normals or UV coordinates) then it gets duplicated on export. So the highest possible vertex count would be 3*triangles for something entirely flat shaded, or every single face its own uv island.
Probably switching it to smooth shaded is the fix you need, but you should also consider cutting it into smaller sections.