you don't need to do fifteen hours straight.. you know the game saves your progress right? go away and do your thing then come back and there it is. It's just down to impatience. Play the story through, get Goliath opened up and then sit and do two or three laps. half an hour max and with the credits boost on you get almost 2 million. or take a weekend day and do a longer race and make a heap more. And if you consider it a waste of time then maybe this isn't the game for you.