Douglas Anderson, chief organiser, said the send-off had exceeded all expectations.
"Once again, the people of Glasgow have taken this event to its heart," he said. "We had 9,000 people in 2011, we thought we'd get 12,000 this time and we've got over 15,000. It's amazing. The spectators were lined up over an hour before the start."
Glasgow is among four host cities, along with Barcelona, Copenhagen and Reims.
Scott Taylor, chief executive of Glasgow City Marketing Bureau, said: "To get over 15,000 spectators is beyond expectations. I think we have an Olympic and Commonwealth Games effect at the moment."
Teams leaving from the city included entries from Australia, Malta, the Czech Republic and France, with those taking part in the rally ranging from serious drivers to recreational drivers hoping to enjoy a unique trip.