HISM vs Merge vs ISM in initviews? Optimization

So… I have a large initviews cost (around 3-4ms… for VR it TOO MUCH)
i have (as i think)a 3 possible solution - HISM, ISM and Merge?
as i know - HISM have a separate occlusion culling and other visibility for each instance?
ISM and Merge - 1 for all, but ism don`t have any lods? (or lod applied for all instances ?)
so if i go ISM or Merge method - it would help me down the initviews cost? and HISM - not (just reduce drawcalls)?