RELEASE_NOTES [1] contains no mention of systemd (or at least does not contain that string).
README.TXT [2] also does not contain the string "systemd"
ANNOUNCE.15.0 [3] also does not contain the string "systemd"
If such a 'note' were included in the last release (15.0) it should have been in one of the above three files. So there is nothing in the release that appears to indicate a shift to systemd.