Prosecutors were investigating another 106 people alleged to have taken part in the May uprising, investigators from the chief prosecutor's office told parliament on Monday, the Uzbekistan National News Agency said on its website.
The trial is expected to open on 20 September.
Human-rights groups say more than 700 people were killed by government troops putting down the uprising, which participants say was triggered by rights abuses and poverty.
The authorities put the toll at 187, including 60 civilians.
Investigators said their findings showed that the uprising was "a carefully planned action by destructive outside forces" aimed at creating an Islamic state in Uzbekistan that would "serve their geopolitical interests".
They did not identify the outside forces.
Human rights groups say 700
people were killed in the uprising
They said the 15 to go on trial later this month were the most active participants in the unrest on 13 May, when protesters stormed a prison and seized a government building.
They did not name the suspects who will stand trial.
Prosecutors say the uprising's organisers had chosen an area in neighbouring Kyrgyzstan as a base where foreign instructors, from January to April, had allegedly trained about 70 people for "terror attacks".
Poor rights record
More than 60 armed Kyrgyz citizens also participated in the violence, the prosecutors say.
Of the 527 inmates released from prison during the uprising, 496 have returned to prison, six were killed and 25 are still at large, the prosecutors say.
Uzbek President Islam Karimov, who tightly controls the former Soviet republic, has rejected calls for an international inquiry into the violence.
Karimov's government has long been criticised for a lack of economic reforms and a poor human-rights record, especially the harsh persecution of Muslims who practise Islam outside state-controlled institutions.