Is ONE PIECE episode 515 filler?
Canon No, episode 515 of ONE PIECE is canon.
#515
I Will Get Much, Much Stronger! Zoro's Pledge to his Captain!
まだまだ強くなる！ゾロ船長への誓い
Aired 18 Sept 2011
Mochibayo compiled this list from MyAnimeList's labels, because MyAnimeList's episode data is not reaching us at the moment.