The numbers in your query likely refer to a specific associated with the song's leak history:
While the final version was released on Number 1 Angel in March 2017, several alternate demos and solo versions leaked online between 2020 and 2021. Connection to "XCX World" Charli XCX Baby Girl 01 09 18 15 mp3
Metadata from a leaked rough demo indicates the song was recorded on September 3, 2015 (03/09/15). The numbers in your query likely refer to