Deputy interior minister Abdullah Massoud said it was only a “preliminary toll” and that the blast caused massive damage in the area of Al-Jala hospital.
A security official had earlier said the blast ripped through the hospital car park.
“Fifteen people have been killed and at least 30 were wounded in the explosion of a car bomb near the hospital,” the deputy minister said.
He said the blast “totally destroyed a restaurant and seriously damaged nearby buildings.”
A witness said he heard a “very loud explosion”.
The attack in Libya’s second city, cradle of the 2011 uprising that toppled veteran dictator Moamer Kadhafi, is the latest in a wave of violence that has shaken Benghazi in recent weeks, and comes against the backdrop of political and security tensions in the capital.
Four police stations were bombed in Benghazi in recent days — two on Friday and two on Sunday — causing damage but no casualties.
Benghazi has seen frequent attacks and assassinations targeting security officials since the uprising that toppled the Kadhafi regime.
Authorities blame radical Islamists for the violence, including a deadly attack in September against the US consulate in Benghazi that killed ambassador Chris Stevens and three other Americans.
The latest violence also comes days after the United States and Britain withdrew some staff from their embassies in Tripoli citing security concerns over a flare-up between militiamen and the authorities.
The militiamen, mostly former rebels who helped topple Kadhafi, had surrounded the foreign and justice ministries to press for a vote in the national assembly barring former officials of his regime from holding government jobs.
They lifted the siege on Sunday, ending a two-week standoff, days after the vote was passed by the General National Congress and a pledge by Prime Minister Ali Zeidan to reshuffle the cabinet soon.