Egyptian Minister of Military Production Mohamed EL-Assar (R) attends a Christmas Eve mass at the newly inaugurated Cathedral of Nativity in the New Administrative Capital, Egypt, 06 January 2019. The Middle East's biggest cathedral is inaugurated by Eygpt's President a day after a deadly bomb blast near a church. Orthodox believers celebrate Christmas Day on 07 January, according to the Julian calendar. EPA-EFE/KHALED ELFIQI 
Ahmed Douma was arrested in 2013 on charges of clashing with security forces in Cairo two years earlier, and received a 25-year prison sentence in 2015.
But the court of cassation overturned the ruling in October 2017 and ordered a retrial, which concluded on Wednesday.
In addition to the 15-year jail term, Douma was fined six million Egyptian pounds ($335,000, 290,000 euros), a judicial source said. The verdict can be appealed.
Douma was a leading activist in the 2011 revolt that toppled former president Hosni Mubarak, who was succeeded by Islamist Mohamed Morsi.
President Abdel Fattah al-Sisi, a former army chief who led the military in ousting Morsi, is accused of leading a relentless crackdown on both pro-democracy campaigners and Islamists.
While numerous key activists from the revolution are behind bars, the majority of top figures from Mubarak's regime have gradually been acquitted and freed.
The 2011 revolt saw hundreds of thousands of protesters call for "bread, freedom and social justice" and rally against a regime seen as corrupt and dictatorial.
But eight years on, the majority of experts view Sisi's government as the most repressive in the history of modern Egypt.
In an interview with American network CBS aired this week, the president said Egypt has no political prisoners.
Egyptian authorities systematically deny allegations of human rights abuses. DM