It zipped past $12,000, $13,000 and $14,000 within the past 48 hours before popping above $15,000 on Thursday morning in New York, according to the tracking site CoinDesk.
"Bitcoin now seems like a charging train with no brakes, said Shane Chanel, an adviser at investment services firm ASR Wealth Advisers. "There is an unfathomable amount of new participants piling into the cryptocurrency market."
Bitcoin has suffered a series of steep drops during its epic rally this year, giving investors jarring reminders of its extreme volatility. After breaking above $11,000 last week, it abruptly plunged by more than $2,000 before resuming its climb.
Top economists and business leaders have dismissed it as a bubble: Nobel laureate Joseph Stiglitz said last week that bitcoin "ought to be outlawed." But experts inside the industry predict its rally has a lot farther to run.
Bitcoin's rapid rise this year has been powered in part by expectations that established fund managers are set to start pouring money into the virtual currency as it gains legitimacy.
But a study published this week by Natixis Investment Managers, a major French asset management firm, found that 64% of institutional investors think bitcoin is a bubble.
The digital currency has also gotten a big lift this year from mom-and-pop investors in countries like South Korea and Japan who don't want to miss out on the prospect of further big gains.
Bitcoin is one of many cryptocurrencies, virtual "coins" that are "mined" by computers using complex algorithms.