Trump's envoy John Coale has been negotiating with Lukashenko for more than a year, so far obtaining the release of hundreds of prisoners including opposition figures, activists, journalists and lawyers in return for removing some US sanctions.
Banned human rights group Viasna says 883 political prisoners remain in Belarus, convicted on charges such as extremist activity, incitement to hatred or insulting the president.
Lukashenko, an ally of Russian President Vladimir Putin, has ruled Belarus since 1994.
He denies there are any political prisoners in the former Soviet state but has engaged with the US administration in order to get sanctions relief and ease his international isolation.
Lukashenko's office said the 15 newly pardoned people included 10 women, and 13 of them had "committed crimes of an extremist nature".
It said the pardons were granted after they asked for clemency and expressed remorse.
The releases represented further gradual progress towards Coale's stated goal of freeing all the remaining prisoners this year.
During his visit last week, he won the release of 25 people including prominent journalists and activists - far fewer than the 250 who were freed during his previous trip in March.
Analysts say Lukashenko is taking a tougher line in the talks, frustrated that the removal of some US sanctions - especially on potash, a key export earner for Belarus - has not been matched by the European Union.
Lukashenko has also demanded the release of about $US43 million ($A61 million) of frozen Belarusian assets that he says are "stuck" in Citibank, and Coale promised last week to address this.
Citi has declined to comment.
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