[breakerbox]

The only thing I’ve put together from light searching on GitHub might be to do with the fact that 15 and s15 can be used to describe school years (s for spring 15 semester) and a lot of people post assignments to GitHub.

15 is also a common number in coding problem sets that people post to GitHub. It’s a stretch but it might be something to do with 2015 being a year that has a lot of coursework commits, and 15 is a pretty low number (i.e. higher probability a student posts solutions to #1-15 than #1-19).

The same goes for schoolwork. Many people do online MIT and Stanford courses that are from previous years ~2012-2016, but there has been less time elapsed for students to post answers from 2016,17,18,19)

This is mostly conjecture, so I hope someone has a better answer!

[WilliamEdward]

advent of code also came out in 2015... so, maybe?