First and foremost:
You will get a better perfomance by disabling collision and disabling overlap events. Every transform change triggers an overlap check on all of the other overlap-able shapes.
If you need collisions for a player use non-movable custom collision shapes (like built-in invisible wall actor)
also, you will get better perfomance with one “timeline manager blueprint” while all of the spheres track it instead of all of the spheres making their own.
But the best solution for visual-only changes would be to use a material. Then it’s all on the GPU and there’s no tick / timeline overhead. One implementaion is here, but there are plenty of tutorials on that.
Additionaly you can check some performance tips here:
https://www.reddit.com/r/unrealengine/comments/13y9pyk/optimizing_the_game_for_hundreds_of_entities_for/
it’s for entities but a lot of the tips are valid in your case as well.