We know Rockstar tend to spend inordinately long on their games- that’s one of the reasons that more than a half decade separates major releases in all of their franchises. For instance, when Red Dead Redemption 2 finally (hopefully) launches next year, seven years will have separated it from the launch of Red Dead Redemption in 2010.
Now, we can definitively say that by that point, the game will have been in active development for at least three years- Reddit posted the image of Joe Cavers, prominent sound designer in the gaming industry, who has posted his portfolio online, and apparently, he has been working on Red Dead Redemption 2 since at least 2014, which means we can safely say the game has been in development that long (the sound designer seems to have since removed this specific text from his website).
We can also probably assume that he came in during the back half of the game’s development, and that conceptualization and early work on the game had begun at least a couple of years before that- giving us a development cycle closer to five to six years for the game than three by the time it launches.
That is absolutely crazy- but it is why Rockstar manages to hit it out of the park with each of their releases, while their competitors often struggle. Red Dead Redemption 2 is currently announced for Fall 2017 for Xbox One and PC.