High resolution terrain texture outside Unity

Hi! I wanted make terrain for my game but the build-in editor make too many triagles. Soo I exported my terrain to .obj file and optymalised this in blender. But while I wanted textured this, it turned out that the textur have to be very big. So I think that must be any way to receipt quality how in unity when texturs are copping first next to second. How to do this in any program?

Thanks for each help!