I know for sure that it's asian. 

It gave off Japanese vibes, but I'm not entirely sure. 

I remember it being about a girl who died and was trapped as a spirit inside her school. It was mostly likely horror, and might have involved a curse of some sorts? 

I remember an elevator scene in which something horrifying happens. 

The movie didin't air from 2015-2019

It might have been one of the ju-on movies, but who knows. 

There is this movie from 2002 :

https://mydramalist.com/1302-dark-water

with a lot of elements (young girl died, apartment cursed, horror scene in elevator) except the spirit is not trapped inside her school (we saw yet scenes in school) but inside her building.