Mixing 15 fps and 24 fps does not work well because video files can only be at one framerate; the consequence is that clips in these different framerates will look jittery in order to conform one frame rate to the other by doubling frames or omitting frames sequentially.

However, it is true that 15 fps is not ideal for certain kinds of motion. This is why professional stop motion animation is usually shot in 24 fps on twos, wherein two frames are taken at a time so that the bulk of the animation is 12 fps, but occasionally it can be ramped up to 24 fps whenever is needed simply by animating each frame instead of two at a time. I like the look of 24 fps on twos (nearly every professional stop motion film you've ever seen is done this way) and I don't miss the extra 3 fps per second of 15 fps.

Alternately you could do the same thing with 15 fps, mixing and matching it with 30 fps. This should avoid stuttering issues as the computer will just double each of the 15 fps frames. 30 fps tends to look very digital and video-like, though, because of its origins in video technology.

That depends on the camera rig you have, Squid does excellent camera movement, and I believe (correct me if I am wrong) he uses 15 fps.

The rig is irrelevant.  Take a fig walking for example.  You want to pan/track the fig.  The fig will walk at the same speed no matter the FPS.  At 15 FPS the amount of travel the camera will need is greater than the amount of travel needed at 24 or 30.  It simply isn't as smooth.

And Devine - that is the question I was also asking but I didn't realise the confusion until you posted that so clearly.  I am indeed talking aboutg shooting 15 fps - make an AVI - shoot 24 make an AVI - join together in movie maker (or whatever).

The final movie would always be one file, though, which is where the problem resides. The only way around it is to encode the final video in a very high frame rate, but YouTube, Vimeo, and most other platforms would not support that.