This achievement is for surviving 15 minutes on hard.
Originally I thought you had to survive 15 minutes straight. On the other 2 difficulties it is as easy as selecting USA and hiding in the rubble while you do something else like watch youtube or make a sandwich. In this difficulty it isnt that simple as you actually have to run around to avoid dying due to the mass amount of dinosaurs. However I have discovered that the 15 minutes does NOT have to be in one round. It turns out that it is cumulative. In other words if you die after surviving 4 minutes you only have 11 minutes left you have to survive.
*If you die the next round will automatically begin so if you want to you can just leave to do something else and you should have the achievement when you come back.
* You can change the difficulty in options