Thank you for the feedback. The idea behind taking the whole time to drown in the tutorial level was to have the player learn how long they can safely stay underwater for levels like the flooded cave. I did reduce the time in the sketchbook level where the water was only for drowning.
As far as the scene transitions go this is the video that I started with. You should probably do it using a coroutine in code instead of animations, but this is a good place to start. You can look at my SceneLoader script here for how I did it.