It's more than possible to make $15,000 in 4 months with YouTube. Especially now, with certain niches like gaming when the big games are going to be coming out and the holidays.. oh dear. It's the perfect time to make a community channel and just pump out content. The key to YT is just pumping out a lot of quality content the first month, then slowing down and promoting it and also starting up secondary channels. If you had around 2-3K videos pumped out over a 4 month period, you'd definitely be able to reach 25M-30M views, if not even more if the right content got viral (like leaked footage of CoD or Battlefield before it came out), and at that point that could be worth anything from $15K to $40K.
You'd be able to monetize through ads, Patreon, in-video sponsorship ads, selling some products later on, selling shoutouts/promos, and lastly flipping some of the channels.