How fast is "UKismetSystemLibrary::SphereOverlapActors(...);" ?

Hi, Guys,
I looked inside and i know that it calls low level PhysX queries.

The main question is “How fast is it?”
If I have a million objects, can i use it in tick?
If it will be called on server side on CPU it will be fast?
Which algorithm it uses? Something like KD trees? Or its primitive implementation O(N)?