Massive slowdown of the video player in projects with a long duration

I’m currently editing a video that’s about 18h long and I’m close to finishing it, but since the ~14h mark or so the built-in video player is barely usable as playing video files even at normal speed results in nothing but constant stuttering.

I’m using proxy editing and my hardware is also not a limiting factor.

Scrolling over the timeline via arrow keys or using the mouse works just fine, it’s just that playing a video file via the player is close to useless as a means of editing.

Any suggestions?