For this achievement, all you have to do is spend 15 hours in FPS mode. To play in first person mode by pressing
a few times. You can try play through the campaign and multiplayer to get your 15 hours.
This achievement is easly attainable by finding a nice quite alley for your character, plug your controller in by USB and go do something else (overnight or during a shift at work). After your game hits the time mark you unlock the achievements. If you're unsure you have unlocked it, check your notifications.