Load level streams around player?

Is there any functionality I can use to make my instanced sub levels only load themselves if they are X close to the player/camera?

You know their location, you can iterate through your instances (which you would save to an array on creation) and compare distance.

Alternatively, if you need a volume around the level rather than the level transform, you could spawn an actor that would hold the volume and a reference to the level instance and save that actor to the array.