Ive just decided to move the game from my HDD to SSD.
I got a solid FPS boost and much shorter transition times.
I asume that the game constantly has to access the drive to fetch data in order to generate the game environment.
Usually games load the game environment once and keeps it in memory since thats fixed data.
But the procedural generation might require the game to frequently load data and an ordinary HDD might be a bottlenck here.