As a brand new feature brought to GTA V and GTA Online for Xbox One, players now hold the ability to play as their character(s) in the first-person perspective mode. In order to switch between the standard third-person view and the new first-person perspective, you will need to tap the "view" button on the Xbox One controller one or two times.
This will toggle between the various different camera angles in third-person before entering the new first-person perspective mode. As a note, this works whether you are on foot or sitting inside a vehicle (car, plane, helicopter, etc.) Since this achievement requires so much time spent in the new perspective, many players may not necessarily want to work towards this legitimately during their time on the game.
Fortunately, you can grind this achievement out by sitting in a car or standing anywhere in the world - in your house, for example - in first-person mode. Any time spent in this mode during your playthrough will add to the in-game clock that can be found by following these steps: PAUSE > STATS > GENERAL > TIME PLAYED IN FIRST PERSON.
Regardless of which way you decide to approach this task, the achievement will finally unlock once a minimum of fifteen hours have been registered in the new first-person perspective mode.