First of all, big props to you for keeping the scope low. Some people think that they can make something like Undertale in such short time. You're not some people.
The gameplay is simple and fun, but it gets repetitive after playing it more than three times. The first and second gameplay felt fun though. The music kept changing during each gameplay, which was really nice because it reduced the repetitiveness.
The way spirits made silly jokes was fun too! It made me think of them as real people. The game wouldn't be the same without those lame jokes. The sound effects (spirits saying "yaaay!" when they are allowed on the boat) were also a nice addition to the game.
Graphics are OK. They get the job done, and there are even simple animations! Much better than looking at still images.
Overall its a fun game that gets repetitive after 15 minutes, which is the norm for most games made in jams. You could add another mechanic to prevent that, if you plan to keep working on this game. Maybe a minigame where Charon delivers the spirits to the afterlife.
You worked and made something in just 15 days, which is a huge achievement considering this was only your second game. You should be proud of your work and use this as a learning experience. I hope you keep making games in the future. We might even collaborate sometime!