Save the game on a SSD will solve your problem. My old HDD run every scenes like 20 fps and the sound is broken so i tried moving it to a SSD and it works just fine.
Okay so you are right about the steam thing. Game does indeed run a lot better when steam isn't on, but the only thing that changed with the audio is that it's faster as a result of steam being down, but it's still buggy.
Tip to the dev if they are here. Look into the audio issue, fix it. Then look for a way to separate all the scenes in the gallery into different segments as there is no reason you should have to sit through the entire scene with changing camera angles just to get to a camera angle you like only for that one to disappear as well. Surely with animations that good, it should be possible, right?