Just an educated guess here: destroying all the barrels, palisades, torches, and other placeables but leaving the structure intact so that it doesn’t respawn might help. The fortress has a LOT of placeables, enough that it would be an illegal build on every server I’ve ever played on just from placeable count alone. Placeables have a bigger impact on FPS than build pieces because build pieces are instanced meshes and placeables are not.