Hey kyyyte! Would you mind sharing your specs? There's been a handful of reports since last year of some users experiencing low FPS. Lowering the resolution is usually the easiest way to gain additional FPS. Is the low FPS occurring even when the game is sitting at the title screen? Please let me know when you have a moment. Thanks!
The game was originally developed on old-ish hardware and even then FPS would hover between 40-60. On my current hardware I retain complete 60FPS as seen in most of the trailers. 5FPS is strangely low so there must be something else going on which is causing the drain.