360 4K video lagging in unity

HI,

I'm working on an application for oculus go via Unity 2018. Using a 360 video background (4320*2160 at 60fps). Everything is fine and smooth and great in the first scene and stay the same when reloaded and reloaded but when I'm switching to a new scene with the same settings but a different video, it begins to lag strongly. What's the matter. Help, I'm in hurry and I don't know what to do… Thanks