It will obviously be in Fedora 22 Beta very shortly.
What happened since 3.14? Quite a bit, and a number of unfinished projects will hopefully come to fruition in the coming months.
After quite a bit of back and forth, automatic rotation for tablets will not be included directly in systemd/udev, but instead in a separate D-Bus daemon. The daemon has support for other sensor types, Ambient Light Sensors (ColorHug ALS amongst others) being the first ones. I hope we have compass support soon too.
Support for the Onda v975w's touchscreen and accelerometer are now upstream. Work is on-going for the Wi-Fi driver.
I've started some work on supporting the much hated Adaptive keyboard on the X1 Carbon 2nd generation.
In the last cycle, I've worked on triaging gnome-screensaver, gnome-shell and gdk-pixbuf bugs.
The first got merged into the second, the second got plenty of outdated bugs closed, and priorities re-evaluated as a result.
I wrangled old patches and cleaned up gdk-pixbuf. We still have architectural problems in the library for huge images, but at least we're up to a state where we know what the problems are, not being buried in Bugzilla.
A couple of projects got started that didn't reached maturation yet. I'm pretty happy that we're able to use gnome-books (part of gnome-documents) today to read Comic books. ePub support is coming!
Grilo saw plenty of activity. The oft requested "properties" page in Totem is closer than ever, so is series grouping.
I'm a fan
Of the new overlay scrollbars, and the new gnome-shell notification handling. And I'm cheering on co-new app in 3.16, GNOME Calendar.
There's plenty more new and interesting stuff in the release, but I would just be duplicating much of the GNOME 3.16 release notes.