It wasn't 15 min as a DPS, it was longer than 15 min as a Healer. Healers are pretty scarce in queues too so for a Healer to wait that long is an obvious sign that Tanks aren't queueing nearly enough for that dungeon/roulette. Furthermore it has been this way for 50/60 Roulette for quite awhile. That means unless Square Enix offers Tanks incentive to queue for it it will remain this way for that roulette and those dungeons, probably forever.