Fire in the Yaung-hole!

Fly to the plateau with a hut at 61.1, 44.2, where four oil pots spawn at the edge and two more beside the hut. Grab a Highly Explosive Oil Barrel from the pots — if others are actively killing enemies nearby, the pots respawn quickly.

Keybind the oil barrel before heading to the combat zone so you can throw it rapidly without fumbling through your bags or action bar.

Position yourself just south of the blockade at the base of the hill, where Yaungol and mantid fight each other — both factions count as combatants toward the achievement. Wait for a large group to gather, which can reach 25 or more NPCs. Both sides of the clash count, so do not target only the mantid.

Bomb the largest clump once, then immediately spam the keybind to throw a second barrel at the same spot. There is a 3-second grace window in which a second or third barrel still counts toward the same kill threshold, letting you reach 15 kills even if the first barrel alone would not.

If the mobs are too spread out, land and send Protector Yi in to pull them together, then throw the barrel onto the group attacking Protector Yi. The achievement should trigger within a few seconds of the barrels landing.