Just wanted to share my experience with ISM and merged actors.
I seems that ISM is not optimized for mobile VR (or perhaps not for ES2 only?). Where I got 24-35 fps using ISMs, I got my standard stable 58+ fps by merging some actors using Merge Actors tool.
Not to mention I’ve experienced some bizarre issues with streaming levels and ISMs using static lighting, which Epic could not reproduce even with my test case.
Just wanted to let you Gear VR UE4 devs know :o