Question: Which series worked on by Aaron Springer ran from June 15, 2012 to February 15, 2016?

Context paragraphs:
Band Geeks: "Band Geeks" is the second part of the 15th episode of the second season, and the second half of the 35th episode overall, of the American animated television program "SpongeBob SquarePants".  It originally aired on Nickelodeon in the United States on September 7, 2001.  It was written by C. H. Greenblatt, Aaron Springer, and Merriwether Williams, and the animation was directed by Frank Weiss.  Springer served as storyboard director, and Greenblatt served as storyboard artist.  The song "Sweet Victory" by David Glen Eisley was featured in the episode and was later released on the album "" in 2005.

Have You Seen This Snail?: "Have You Seen This Snail?" , also known as "Where's Gary?" , is the third episode of the fourth season and the 63rd overall episode of the American animated television series "SpongeBob SquarePants".  Its animation was directed by supervising director, Alan Smart and Tom Yasumi, written by Aaron Springer and Paul Tibbitt.  Springer also functioned as storyboard director.  The episode originally aired on Nickelodeon in the United States on November 11, 2005.  Actress and comedian Amy Poehler guest starred in the episode as the voice of Grandma.  Musician Stew performed the song "Gary, Come Home".

Pizza Delivery (SpongeBob SquarePants): "Pizza Delivery" is the first segment of the fifth episode of the American animated television sitcom "SpongeBob SquarePants".  The episode was written by Sherm Cohen, Aaron Springer, and Peter Burns, and the animation was directed by Sean Dempsey.  Cohen also functioned as storyboard director, and Springer worked as storyboard artist.  It originally aired on Nickelodeon in the United States on August 14, 1999.

Gravity Falls: Gravity Falls is an American animated television series produced by Disney Television Animation originally for Disney Channel (and then later for Disney XD) from June 15, 2012 to February 15, 2016.

Robertryan Cory: Robertryan Cory (also spelled as Robert Ryan Cory) is an American animator known for his work in character design for series such as "SpongeBob SquarePants" and "Secret Mountain Fort Awesome", the latter of which he co-developed and earned a Creative Arts Emmy Award for "Outstanding Individual in Animation" at the 64th Primetime Creative Arts Emmy Awards in 2012 for.  He has recently worked as lead character designer on season 2 of "Gravity Falls", and is now working on Aaron Springer's forthcoming Disney XD series "Billy Dilley's Super-Duper Subterranean Summer".

Aaron Springer: Aaron Springer (born September 5, 1973) is an American cartoon director and storyboard artist.  He is best known for his work on the Nickelodeon animated series "SpongeBob SquarePants".  Springer has collaborated with various animation veterans such as Genndy Tartakovsky, Paul Rudish, Rumen Petkov, Stephen Hillenburg and John Kricfalusi.  He created numerous pilots for Cartoon Network and Adult Swim that, although never made into full series, have developed cult followings. Springer's cartoons are unique for their inclusion of extended gags, anthropomorphism and off-model poses.  He is also the creator of the Disney XD original series "Billy Dilley's Super-Duper Subterranean Summer", where he voiced the main character Billy Dilley.

SpongeBob SquarePants vs. The Big One: "SpongeBob SquarePants vs. The Big One" is the 11th episode of the sixth season and the 111th overall episode of the American animated television series "SpongeBob SquarePants".  The episode was written by Aaron Springer who also directed the stoyboards, Paul Tibbitt, and Steven Banks, and the animation was directed by Andrew Overtoom and supervising director, Alan Smart.  The episode was part of the series' tenth anniversary celebration in 2009.  It features guest appearances by Johnny Depp as the voice of Jack Kahuna Laguna, Bruce Brown as the narrator, and Davy Jones as himself.  It originally aired on Nickelodeon in the United States on April 17, 2009.

Andrew Overtoom: Andrew Overtoom is an American animation director, writer and photographer/cinematographer best known for his work on the Disney animated television series Billy Dilley where he was a Writer and Animation Supervisor for Creator/ Executive Producer Aaron Springer and Supervising Producer Clayton Morrow, as well as the Nickelodeon animated television series "SpongeBob SquarePants" for which he was nominated for the Emmy Awards in 2004, 2007 and 2011. " My Life with Morrissey" is his award winning first feature film, which he wrote, directed and photographed, and is distributed by MVD

Billy Dilley's Super-Duper Subterranean Summer: Billy Dilley's Super-Duper Subterranean Summer (also known as Billy Dilley) is an American animated television series created and executive-produced by Aaron Springer, an animation veteran whose extensive credits include working on "Dexter's Laboratory", "SpongeBob SquarePants", "Samurai Jack", "The Grim Adventures of Billy & Mandy", "Gravity Falls", "Wander Over Yonder", and the current run of "Mickey Mouse" shorts.  Springer was also behind the Cartoon Network pilots "Periwinkle Around the World" and "Baloobaloob's Fun Park", and the Adult Swim pilot "Korgoth of Barbaria".  The show premiered on Disney XD on June 3, 2017.

Korgoth of Barbaria: Korgoth of Barbaria is a pilot episode for what was originally planned as an American animated television series created by Aaron Springer, a storyboard artist, writer and director for "Dexter's Laboratory", "The Grim Adventures of Billy & Mandy", "Samurai Jack", and "SpongeBob SquarePants", who previously created another failed pilot at Cartoon Network Studios called "Periwinkle Around the World", and is now the creator of "Billy Dilley's Super-Duper Subterranean Summer" on Disney XD.  Genndy Tartakovsky, creator of "Dexter's Laboratory" and "Samurai Jack", directed the animation for the pilot, and was not the only time he's worked on a pilot created by Springer, as Tartakovsky also produced and directed "Periwinkle Around the World".

Supporting paragraphs: Billy Dilley's Super-Duper Subterranean Summer Gravity Falls
Answer: Gravity Falls