For the slow framerate, I found that the camera that takes a picture of you before starting the game must be enabled: if disabled makes the game run slow; to enable/disable, I followed the demulshooter wiki.
"Camera can be deactivated in the TEST menu (Main Menu → Option 1 → Option 1 → Option 5 → Small option to the right of the blue text at the bottom)"
To change that small option, you have to use arrow up/down, then in the line below move with arrow right to the last option at the right and return to previous menu