You can toggle here if you want to hide certain game object spawns to be hidden in the hierarchy.
Objects will still be rendered in the scene view, but the editor will stop rendering the outlines and colliders.
This increases editor performance and reduces the visual clutter on the terrain.
To activate this you simply need to spawn the object from the spawners, and then under the terrain click on the
(Gaia Game Object Spawns).
You can still see the objects in the scene view just the outlines are gone and you should be able to gain some performance.
You can also apply this to all terrains!
To turn all of them back on you can click on Show All and then hit Apply Now.