Exact same issue, unfortunately I also have only 8gb RAM so it's even worse for me. Definitely a memory leak somehow embedded into the save though, I can run DOS2 side by side w/ Afterburner and watch memory increase by ~100mb every 2-3 seconds until it hits 7,5gb or so and crashes. Obviously no such issues when starting a new game. Also the problem with increased loading times, at the start that was the only oddity - but as time went on it became worse and worse until the game is no longer playable.
I suspect the issue is more or less universal if you spend too long in Fort Joy, I guess I shouldn't have taken it slow and steady on Tactician difficulty as I'm ~8 hours in and have still not escaped. Maybe it's a fail safe implemented to make us play quicker
