This achievement is for rescuing 15 survivors from Zombies in Harran.
As travel through the map, you will frequently encounter random events as seen in both videos below by a flashing blue circular marker (shows up on minimap).
These markers can mean a number of things and are not always for rescuing a survivor from a zombie. They may also be for a street fight with two enemies, a rescue from an enemies men or a random shop to buy and sell items.
For this achievement,
we need to be rescuing a survivor from zombies. They may be in the street being attacked, or surrounded in a building. Simply kill the zombies (marked by a red arrow on your minimap) and you will get credit toward the achievement once you are able to receive your reward.
Given the glitchy nature of this achievement and several people reporting they were not getting credit towards this achievement on Old Town, it is highly recommended to complete this achievement BEFORE leaving the Slums for the first time. (Thanks Elite1111111111 for reminding me to update this solution with this information!)
Zombie in a building video:Zombie in the street video:These are
my own videos I uploaded from my own gameplay.
Thanks to ChronosKaos for help editing this solution.