The Church of Scotland-led memorial at Cathcart Old Parish Church saw wreaths laid and the flags of the New York police and fire departments flown.
It was led by Rev Neil Galbraith with Christians and Muslims involved in readings during the service.
Representatives of the Scottish Ahlul Bayat Society, a faith group which works in the Shia Muslim community, laid a wreath, read from the Koran and lit one of 15 candles.
Police Scotland Deputy Chief Constable Ruaraidh Nicolson and local politicians also laid wreaths.
Rev Galbraith founded an aid charity called Glasgow the Caring City which sent a disaster relief team to New York in the days after the terrorist attack.
He said around 70 American families have been flown over to Glasgow in the last decade for “therapy” holidays organised by the charity.
His church also has a piece of marble and part of a girder from the Twin Towers.
He said: “It is important to mark the 15th anniversary of the September 11 attacks because the worldwide consequences of that day have been immense.
“It is significant that the Scottish Ahlul Bayat Society are taking an active part in the service as equal partners.
“Their attendance sends out the message that, as a community, we are all in this together.”
He added: “There will never be another memorial service like this because a lot of the people who were involved in 9/11 are getting a lot older and might not be here for the 20th anniversary.
“With the passing of age, we must pass on to the young folks a modern Scotland, a more caring Scotland which has a respect for each other’s faiths and is diverse enough to build bonds which can never be broken.
“And what better time to do it than on the anniversary of the day when the world changed and almost imploded, except for the fact that people of faith, humanity and compassion worked even harder and loved even stronger to ensure it would never happen.
“There is a bit of New York in all of us.
“That no matter what happens, with faith we can be stronger and united, you can love again.”