First Slice does not have any of the assets from Part 2, and vice versa so trying to load a save from one game with another will cause an error. The complete edition is coming in October and will include all previous parts and the final chapter, as well as some additional content and features.
Viewing post in Jill O' Lantern: First Slice comments
In First Slice, after a certain point it got to a point it got to something the game itself is Part 2 of the game and I do not own Second Helping. The last thing that happened the crash is Vivian running from the camp after figuring out the party goers were spiked with the drug Seven Sins and then the game crashed.