Far Cry Primal

You need the Owl: Attack Skill for this achievement. You can reduce the cooldown to 40 sec but it is not necessary in my opinion. The Owl: Weapon Drop Skill does not count! Only Owl: Attack counts. You can do this everywhere on the map, best places are outposts or bonfires. Use your owl, identify a target and use RT when the game tells you (Owl: Attack). Repeat this 15 times during your playthrough and the achievement is yours.

Animals counts also as enemy (thanks to B0ngAAA in the comments)

I want to share my experience to people who (like me) played the game in survival mode and realized at the end that this achievement was the only one unobtainable. I thought it would take me several hours to restart the story, unlock the skills and get this one, but it is actually pretty simple. Here is a little roadmap :

- Restart a game, set every parameters on easy and disable the gathering animations.
- Remember to skip every cutscenes to progress faster (the first one appears to be unskippable).
- Gather as much Alder Wood, Slate, and Reed as you can, as well as at least 2 Wolf Skins: you will need it to build Tensay's hut and get access to the skill.
- Keep at least 1 Skill Point (3 is better, 6 would be great but not necessary).
- Play the main quest until you go get Tensay to bring him to your camp.
- Once he is at your camp, build his hut (once is enough).
- Now, get to your Skill Tree and unlock Owl: Attack I (1 SP), and Owl: Cooldown I (2 SP) if you have enough Skill Points. Keep unlocking this tier if you have some more.
- Then, go into Oros, preferably to an outpost or a bonfire, and take out every Udam with your owl. Kill any wandering Udam or beast that you encounter this way as well.

I went to the Nakuti Bonfire, hoping to meet a few enemies, but this one is empty. So I went to the other one, south of Nakuti, found a few Udam there, and finished my kill count with some enemies from the outpost east of there.
I killed a few beasts on my way to each location, as well as some wandering Udams.

It took me a bit more than an hour to make the achievement pop, and I wasn't rushing at all, so this one is not that hard to get.

Have fun!

This achievement requires you to use the initial attack skill of the owl that is unlocked through Tensay. Killing 15 enemies counts much the same as it does for the companion pet, it counts as opposing tribe members or beasts. Simply kill 15 this way and the achievement should unlock for you.