[Q] Why when doing uv mapping switches textures result in a loading hickup

Ive been wondering why each time why im uv unwrapping and i load a texture is see the rotating beach ball on mac. It seems blender needs to load something. It doesnt take realy long 1-2sec maybe longer. But its always the first time when i go into editting and asign a texture to the selected mesh. Once ive done this it doesnt seem to slow down.

Is this due to the size of the texture? Is it better to model with “texture: memory limit on”?