That was soon followed by a mass rebuild against glibc-2.32 which is a pain of you're running current or just installed somenthing like Slackel which is tracking Slackware-current. Never mind, that's why it's called a testing ground. Currently the kernel is Linux 5.10.12. With such a modern base that seems like a good position for an upcoming release.
I have to admit that with stable getting so old I have switched to other distributions years ago and which are also running nicely. Mostly based on another old favorite, Debian/Devuan, but also Mageia and openMandriva for testing. They didn't make the cut though. Until recently I got my Slackware fix only via alien's LiveSlak project, the Plasma edition, which is in all honesty a good way to run Slack and almost a distribution in itself. You get a ready made vanilla Slackware enhanced by a few choice packages from alienBOB. In between some quick testing of where development was at with a quick install from a Slackware FTP server and since recently the release of the aforementioned Slackel 7.4 with Openbox, a perfect base to add Plasma packages.
It looks like the wait could be over this year. I have no idea how Pat is paying his bills but he obviously isn't relying on sales of DVD's if he can wait this long. In the meantime you might want to prepare for compiling Cinnamon Slackbuilds. As times move on I think this is now a better desktop than XFCE is and the best and most full-featured in the GTK universe. If KDE Plasma isn't quite your thing. So although most of the GNOME build projects that used to be there to provide GNOME 2 have gone away we still have choices. There is the Cinnamon on Slackware project, the MATE for Slackware project, i.e. MATE Slackbuilds, and Dlackware - GNOME 3 for Slackware. The Dropline GNOME project has survived the transition and is also offering GNOME 3 for Slackware (without reliance on systemd).
In anticipation I once started reposting the changelogs here in 2018 but then stopped as it became apparent no new release was fortcoming any time soon. I won't be doing that again. Everyone can follow the changelog here. So is 15.0 finally coming up still this year? Only time will tell. I guess Pat is following the same mantra as Debian folks do - it's ready when it's ready.
Do they still place bets on the release date in alt.os.linux.slackware?