Bell was suspended without pay for conduct "dishonourable, prejudicial to or against the welfare of the league or the game of hockey," the league said in a statement Wednesday.
Bell, 27, pleaded no contest to his criminal charges last month after being arrested last September in California. He is due to serve six months in a California county jail at the end of the 2007-08 NHL season.
In suspending Bell, commissioner Gary Bettman said the player had avoided a longer ban because of "extraordinary strides in his rehabilitation."
Bell, a former first-round draft pick who is now a checking forward, has said he hasn't had a drink since the incident.
The 15-game suspension will begin once he's cleared to return by the two doctors who run the substance abuse program jointly run by the league and NHL Players' Association. Bell was suspended indefinitely Sept. 4.
"Playing in the National Hockey League is a privilege, and with that privilege comes a corresponding responsibility for exemplary conduct off the ice as well as on it," Bettman said in a statement. "Mark Bell will serve jail time following the 2007-08 season after pleading to felony and misdemeanour charges stemming from an alcohol-related automobile accident that caused an injury. He also left the scene of the accident. Such conduct is a violation of our covenant with our fans, and to the game, and is prejudicial to the welfare of the League.
"However, over the past year, Mark has made extraordinary strides in his rehabilitation. This positive progress was a material factor in reducing what could have been a lengthier suspension. The NHL supports Mark's commitment to learning from his past mistakes and his efforts to move his life forward in a positive direction."
Bell was arrested after his car rear-ended a pickup truck in an early morning accident in Milpitas, Calif., a town in the San Jose foothills. The 40-year-old driver of the truck received head injuries and cuts.
The Maple Leafs acquired Bell in June along with goaltender Vesa Toskala in a trade with the San Jose Sharks.