The timing required to achieve this makes it a little more challenging than "Rushing Roulette". You need to start by getting a stealth kill. This alone limits the locations in which you can get this done as it is quite tricky to stay undetected in a lot of locations. The best gear for this would be a grenade launcher and a powerful pistol. Once you have killed the enemy using a stealth you need to run on and get a melee kill, you should be able to "soften" the enemy up with bullets to make it a one punch kill, but this is risky. The next you need is a headshot. You can use any gun you like for this, but I would suggest using a powerful pistol (or any pistol if you are up against standard enemies). The final kill needs to be an explosive kill, you can use a grenade but these are too slow. Grenades take time to throw and then time to blow up. By using a grenade launcher or some other gun with explosive rounds, you can quickly get the kill without too much a delay and less risk of missing.
Defeat enemies with a stealth attack, melee attack, headshot, and explosives, in that order, in 15 seconds