It doesn't provide the 15 second buff. Whichever control ability procs it also limits the buff length. If the control ability ends or enemy dies, then Checkmate also ends. Example: an enemy dies 1 second into a Tractor Beam. Checkmate ends after just 1 second.
Sorry, are you trying to get the post removed because I tried to get this addressed 3 weeks ago and am mentioning it again? Do you consider waiting weeks to be frivolous spam or something?