900k test
As a number 900K in the year 2020 is not a lot or even the use of 8k textures but to give an educated response there is need for more information.
What application are you importing from?
What is the planned purpose, intended use?
Are you importing morphs?
In general yes it can take a long time to parse an FBX due to the amount of data the host app sends to the format and what you chose to import into UE4.
In the example on the other hand was imported using the DS to unreal 4 bridge and took no more the 5-10 minuets with out morphs