[$] Development statistics for the 6.15 kernel

The 6.14 kernel development cycle only brought in 11,003 non-mergechangesets, making it the slowest cycle since 4.0, which was released in2015. The 6.15 kernel, instead, brought in 14,612 changesets, making itthe busiest release since 6.7, released at the beginning of 2024. Thekernel development process, in other words, is back up to full speed. The6.15release happened on May25, so the time has come for theobligatory look at where the changes in this release came from.