I just finished playing Episode 3 (Jill Saves the Prince) which I did to refresh my memory of it. This one is quite a bit hard than the previous two, with many tight situations and instant-death traps (spikes on platforms in mid-air are the worst). Many levels I had to restart multiple times, and some of them are quite long. Still, I managed to beat it playing leisurely over a couple of evenings.
This is where the game’s design, where the level is not reset upon your death plays nicely. These hard levels would have been ten times more frustrating, if you had to recollect all the keys and kill all the enemies again each time you died.
The third episode only has 15 levels (and really 14, since the last one is just the ending), but they are longer (and harder), so it does not feel shorter than the earlier episodes. Quite a good game, and the extra difficulty makes it a game you actually have to try to beat, rather than being able to wander through it half-mindlessly like the first episode (and somewhat the second).