What is Frame Doubling in Action Cameras?
The term "frame doubling" is occasionally used to describe the result of animators who "shoot on twos".  Namely, when an animator draws only every other image for a given frame rate, the image is displayed twice before the next image is displayed.  That "frame doubling" is an observable property of the animation, but it is not the key idea.

The key idea is that frame rates can be subdivided (shot on ones, twos, threes, or even fours) and the look and effect of each can be appropriate for a given instant.  Generally, lead animators generate key frames and junior animators (or computers) generate the in-between frames.  Shooting on ones requires generating twice as many in-between images as shooting on twos.  But it also creates a smoothness that may or may not better serve the aesthetic of the animation.  Nick Park's classic Wallace and Grommit animations look "right" because of frame doubling.  Pixar's Toy Story films look "right" because they shoot on the ones (and integrate motion blur on every frame to look as if shot on a cinema camera).

I would argue that a camera that shoots at 1/15th of a second and then doubles those frames for a 30fps playback will create a highly stylized look that combines (in a "wrong" way) the motion blur one would expect from shooting on the ones with the pacing of shooting on the twos.  As Blues music teaches, the wrong note at the right time could be the right note.  But generally, animation shot on twos rarely integrates motion blur as such would be "too obvious".  So if going for a frame doubling effect, one should use a small shutter angle, like 30 or 45 degrees, not 180 or 360, when shooting 15 fps.