An interesting comparison is to look at how long it took gold to be accepted, in various human eras, since both Bitcoin and gold are emergent monies (unlike fiat). Keep in mind, gold had a 5,000 years head start.

Granted, information travels much faster now with the Internet. But I think 10-15 years is still on the overly optimistic side. Bitcoin probably needs to be tested a few more times in crisis situations. People need to see how it holds up against other currencies with their own eyes, and learn the hard way not to bet against it, again and again and again. Only then it will be widely accepted.

I'd give it 30-50 years. In 50 years, the majority of people alive would have been born After Bitcoin (AB).

(And even after that, it still might not count as a "failure").