” I like the results Twixtor gives me in super-slo mo when I set its frame rate input to 15 fps”
If you set “Input Frame Rate” in Twixtor to 15 and your comp is 30 FPS, then what happens is that Twixtor will skip in source time space half the frames,
That is if you have frames 1,2,3,4,5,6,7,… and 50% slowdown
Twixtor will make inbetweens using frames 1 and 3, then 3 and 5,… rather then 1 and 2, then 2 to 3, then 3 to 4…
Pierre