'15 second' stunlocks? I can explain 20 second if perfectly timed and coordinated. Work up 3 combo points, vanish, cheap shot, talented gouge, kidney shot. Done. Cheap shot and kidney don't share cooldowns, and getting 3 combo points is pretty easy with SS, SS, thistle, SS, vanish.
edit: and 'perfectly timing' is relatively easy with stunwatch/ccWatch/Carnival running
edit: and 'perfectly timing' is relatively easy with stunwatch/ccWatch/Carnival running