Alad  filed a deletion request for mate-desktop-1.15-gtk3 :
"The submitted PKGBUILDs MUST NOT build applications already in any of the official binary repositories under any circumstances. Exception to this strict rule may only be packages having extra features enabled and/or patches in compare to the official ones."
 https://aur.archlinux.org/account/Alad/  https://aur.archlinux.org/pkgbase/mate-desktop-1.15-gtk3/
Request #5973 has been accepted by jleclanche .