It took less than five minutes to take care of everyone.
It could be that the mercenaries had a lot of suppressed rage that they were killing everything in sight. By the end of the slaughter, they were covered with blood and bits and pieces of their ice swords were left in the bodies of their victims.
Although the guards were decent at combat, they did not have a strong will to fight and merely tried to escape. However, the gas trapped them within; they were like fish on a chopping block, one by one they were cut to pieces.
The mercenaries had gone so berserk in their pursuit of bloodlust that Benjamin had to summon a spell to bring them back to their senses. "Alright now, the enemy has been eliminated." He stared at the mercenaries and exclaimed, "We have to clean this place up before the other teams find out."