The whole thing? The only point to preordering when games are available digitally is to get preorder bonuses. If you really want the preorder bonuses, then there is no reason not to wait as long as possible when you know more about the game. With Destiny 2, we know nothing about the game mechanically other than the fact that it is a sequel to Destiny 1, and the only preorder bonus is early access to the beta, which will be made public soon after anyway.