While the game has been completed in less time, this speedrun specifically doesn't make use of a glitch that allows players to skip a large chunk of the campaign's second half.
Kahmul plans to shave off even more time in a future playthrough, noting that this speedrun "was a really bad run. That was a really bad run. It was so bad."
Have you been able to complete Dark Souls? I'm afraid to even try, never mind speed through the game.