It’s like a math problem as much as it is a tone and feeling problem. You only have about 23 seconds or so to find a piece that evokes the right emotion, flows with the scene, and is in the right key. Which means you’re probably gonna have to edit, cut, and stretch other pieces to make that all work.
Here’s a low-res, and lo-fi mockup I did.
Problem is, that music piece from TFA’s credits was already used in this edit, for the ending on Tatooine. I think that music is pretty much perfect in it’s current position, so I wouldn’t want to revert it back to the reused Force theme that was in the original movie.
I’m thinking some remixed version of Rey’s theme would be the best fit for the ghost scene. I’m gonna look on YouTube to see if there’s any versions of the theme that fit the moment.