Booted into my MX16 install to update the new gpg key.
Here are some nice uses for flatpaks in MX15/16, which is Debian Jessie-based (gtk+ 3.14)
1. running Lollypop music player
2. installed flatpak version of oomox to create a dark numix theme with the colours of adapta-nokto
The actual Adapta theme is not compatible with gtk3.14, and of course from within oomox, I can't generate themes based on Materia (the closest theme to Adapta) because Materia is also not compatible with gtk 3.14.
But numix is fine as it exists in Debian Jessie/gtk3.14. So I created an adapta-ish numix theme and generated it with the option to generate both 3.18 and 3.20 compatible versions. Looks like the 3.18 version of theme still works with gtk3.14. Don't choose the option to generate theme in "current" gtk version, since my oomox flatpak version uses gtk3.28 runtime (and yes, the "current" version is totally broken in MX15/16 - I tried).
XFWM theme is rich's "borders" theme, for the grabbable edges and border outlines in the cursor highlight colour.
Icons = Numix-Circle, now available in MX repos.
https://imgur.com/g5tkJlT