Alphabet doesn’t disclose how much money YouTube is making, but RBC Capital analyst Mark Mahaney estimates YouTube’s annual revenue has reached $10 billion and is increasing by as much as 40% a year. The growth makes YouTube “one of the strongest assets fundamentally on the Internet today,” Mahaney wrote in a research note this week.
But I have a hard time believing it wasn't profitable in 2015 either. Sure, if they re-invest most of it and pays out the rest to youtubers as a way to market the platform then you can pretend it is breaking even.
Oh, and yes, the difference in ads between now and 2015 is huge. Likely close to an order of magnitude where I am, but that probably greatly varies depending on which market you are in.