Work for the album began to show in August 2015, when the single "Classic", released for their So Classic EP, was re-mastered and released as a 2015 re-release, adding new feature vocals from Fetty Wap along with POWERS. Afterwards, the duo went on to uploading a brand new music video for their collaboration with Alex Newell, entitled "Collect My Love" and was classed as the second re-release from their So Classic EP. Both songs from the EP were considered to be a part of the new album at the time.

In the late months of 2015, The Knocks released a new single which was the first song outside of the So Classic EP and other projects that they had previously work on, which sparked much interest about whether or not the duo was working on a new project. It was titled "I Wish (My Taylor Swift)" and was collaborated with Matthew Koma. It was eventually released in September 2015. The trailer for their debut album was released on their YouTube channel in November 2015, announcing it under the title 55. This teased the release of another single, entitled "New York City", featuring vocals from Cam'ron, and was released the following month. Also in the same month, they re-released their official video for their 2013 single "Comfortable", featuring vocals from X Ambassadors, which was originally released under their 2013 Comfortable EP, and was classed as being another 2015 re-release.

...
Wikipedia