But court president Fawwaz Bakur commuted the sentence against the only one in court, Jordanian Ahmad al-Rayati, to seven and a half years with hard labour "to give him a chance to improve himself and because he is a bread-winner", the court said.
Riyati, 35, was among 15 people on trial since October. Eight of the absentees were also given 15 years but one was killed in a shootout in April.
The remaining six, all Jordanians who lived in Iran, had died under mysterious circumstances and in an unidentified location, prosecutors said in March, and Bakur dropped charges against them.
One of the absentees sentenced is Najm al-Din Faraj Ahmad, also known as Mullah Krekar, the founder of Ansar al-Islam, or Supporters of Islam, who has been cleard in Norway of charges of funding terrorism and inciting murder.
Al-Rayati was specifically charged with having received military training in Afghanistan and training others in Tehran to "prepare poisons and produce explosives for assassinating heads of the Jordanian intelligence service".
He was arrested by US troops in Iraqi Kurdistan during the US-led war on Iraq in March 2003 and extradited to Jordan.
Al-Rayati denied all the charges against him and interrupted the verdict by shouting at the court.
"I am not a criminal. You are the criminals," he said, adding that he wanted to leave Jordan to live in Rafah, in the Gaza Strip.
Mullah Krekar is on a US list of terrorist organisations, alleged by Washington to be linked to al-Qaida and having mounted attacks on US-led forces in Iraq.
"I am not a criminal.
You are the criminals"
Ahmad al-Rayati, defendant
in state security court trial
On Tuesday Norwegian prosecutors in Oslo dropped their case against Krekar citing lack of evidence, but the United States said it still had serious concerns about him.
He had been the target of a Norwegian police inquiry since September 2002. Among other allegations he is suspected of involvement in a conspiracy to murder Kurdish political rivals and funding of "terrorist" organisations.
But Krekar, who has been living in exile in Norway since 1991, still faces an expulsion order for posing a threat to national security and violating his residency permit by returning to Iraq several times.
He founded Ansar al-Islam in December 2001, although he insists he has not led the group since May 2002 and denied all the charges against him.
Ansar al-Islam used to control a small group in northeastern Iraq before it was pushed out by US forces in late March last year. It then allegedly had between 700 and 900 members.