A majority of The Beatles’ songs were relatively short because that’s what fits better for radio play. Besides ‘Hey Jude’, most of their hits were three or four minutes. In one of his more experimental modes, Paul McCartney developed a 15-minute song that he got The Beatles to play with him. It’s still never been released, but the former Beatle said it could see the light someday.
There are many rumored, unreleased songs from The Beatles that fans have been scouring for. One of these mythical tracks is “Carnival of Light”, an “avant-garde” 15-minute instrumental track created by McCartney. The song emerged when David Vaughan, a friend of McCartney’s, asked him to record music for an event called The Million Volt Light and Sound Rave or the Carnival of Light Rave.
Source: Ross Tanenbaum/cheatsheet.com