I had framerate issues in the part with the big spikes, as well as in the room with treasure chest shown in the screenshot, but the latter part wasn't consistent about it. The part where it faded to black after she was captured also took a really long time. I wasn't sure if the game had frozen.
I don't think it's a good idea to preserve the player's health after a cutscene. Even if the checkpoints will bring the health back, it still doesn't feel good. I think the part with the electric eels could've also used some form of mid-room checkpoints as well. That section ramps up absurdly quickly, especially for how short this demo is. It also doesn't help that most of the dangers up to that point can be literally ignored.