Incremental Processing of Newly Loaded Levels
Starting with Unreal Engine 4.15, the texture streamer processes the level data incrementally, so just a little bit each frame, between the time they are loaded and the moment they become visible. Previously,
this processing would happen in the frame the level became visible and could generate some noticeable hitches while doing so.
The amount of work processed each frame is controlled by
r.Streaming.NumStaticComponentsProcessedPerFrame, which has a default value of 50. Setting 0 for this value will disable the
incremental work and it will make the system behave as it did prior to 4.15.
It's important to mention that the incremental level processing will only apply to components with their Mobility set to Static. Movable components have always been processed incrementally in the engine tick.
Once the incremental processing completes, no more processing will be required before the level becomes visible. If it becomes visible before the incremental processing completes, then all pending work needs to be
finished immediately and there could be a small hitch when this happens.
You can investigate incremental processing by running the console command:
Stat Streaming SortBy=name
The cost gets included in the category Update Streaming Data.