According to Slackware-Current changelogs, Current can be considered 15.0 "alpha 1" since February 15, 2021. They also say that they wait for a new release of Firefox compatible with the latest Rust compiler, plus "a few more scheduled upgrades". So I guess 15.0 may not be as far as a few months more, but we will see.
My complaint about 15.0 is the introduction of elogind, a crappy login daemon extracted from systemd as a standalone package. Well, at least it's not systemd - otherwise I would already be migrating to another distribution or FreeBSD. They wanted to do so in order to have Gnome and KDE, the two desktop environments dependent to systemd. I couldn't care less about those resource devours, but it seems they want them. The part I don't like is elogind would be in your system even if you don't have KDE or Gnome installed.
Other than that, it seems a nice new release with (finally) a up-to-date gcc 10.2, considerably improved to the one used in 14.2.
Talk about other linux distributions, or even other OSes.