Check out whether any of the following help
https://doc.babylonjs.com/how_to/optimizing_your_scene
https://doc.babylonjs.com/how_to/caching_resources_in_indexeddb
https://doc.babylonjs.com/how_to/optimizing_your_scene_with_octrees
@JohnK before the move works fine, when u added ur line it is so slow
If this is the case remove my lines.
Alternatively see if it is any quicker when after converting the sets to arrays and iterating over arrays not sets https://playground.babylonjs.com/index.html#KI8BJH#33.
If that does not work then other than checking out the optimizing suggestions above I am out of ideas.
yes it still slow !
here I tried to create directly an array and then push meshes without sources but it still slow :
https://playground.babylonjs.com/index.html#KI8BJH#34
PS: I can’t remove your lines cuz the invisibilty of meshes inside seems perfect, thank u dud 
about the “slow move” I’ll try again maybe it resolves
Smart change to array from set.
Note line 24 where I changed 30, 30 to 5, 5 to see if that speeded things up, you may want to change it back to 30, 30
Line 217 should now be new Array() not new Set()