is demon slayer: kimetsu no yaiba episode 15 filler?

Their next destination is to the north-northeast. Tanjiro and Nezuko head to Mount Natagumo along with Zenitsu and Inosuke.

The mountain is full of spiderwebs and is swarming with spiders... Leaving behind a frightened Zenitsu, Tanjiro and Inosuke make their way up the mountain, where they encounter a fellow Corps member entangled in spiderwebs.