Strange...
For me the syria map is super smooth in VR.
Running on 1.5 PD on Rift S, ASW enabled, MSAA 2x, and experimental "stereo Frustum Culling" enabled.
But I also play with only vis.range on medium and without ground shadows. (building and tree shadows)
Edit: Terrain Textures may have a big impact. Big difference on fps between high or low on this map, as far as i noticed.