1500 hours is 62 days. Homeboy is a tryhard, but not quite on MMO levels of no life
To spread it out a bit more, playing one hour every day on weekdays and two each weekend would be 9 hours a week. At that rate it would take over 3 years and 2 months to reach 1500 hours. Since he's a second year in high school he would have had to start in second year of middle school at the latest.
So not implausible, especially considering he's enjoyed being popular since elementary, but still super dedicated. Plus he also has to make time for hygiene and exercise and whatever else he might want to do in his freetime. Probably going out to be fawned over by girls.