culling gizmos in scene view

Hi, I've made an open world with many gizmos displaying a complex waypoint system. When the gizmos are active, moving around the scene view is very slow.

I'm trying to develop some sort of culling system that will only display the gizmos within the scene view bounds but am having no luck succeeding.

Would anyone be able to spell out how I should go about doing this? It would be greatly appreciated. I'm pretty new to gizmos and have never implemented my own culling system.

Thanks!