In UEFN, one optimization approach for improving level memory usage and performance is to convert Static Meshes to HISM.
In this article, we’ll introduce a semi-automated tool you can use when converting to HISM/ISM.
https://dev.epicgames.com/community/learning/tutorials/y14n/fortnite-hism-ism-batch-convert-static-meshes-placed-in-a-level-to-hism