I have a big map that a sun can’t completely make shadows on
And the problem is?
Typically you do not need dynamic shadow on a complete scene, just in a small but visible area around the camera’s focus.
As usual you need to find a balance between resources and effect.
The usual solution is to parent the sun object to the camera/player object so that it moves where the shadows are needed that being where the player is.
You don’t actually want to parent it though, because it inherits rotation as well. You should use python script to copy player/camera x,y,z and add the delta vector (to not move it in player location because you want it on the sky) to set the sun lamp position. If you’re not good with python you might also just vertex parent the lamp to player mesh.
Parent to vertex