The police said that the accident took place near the Technical College in Katukurunda, Payagala.
Police Spokesperson ASP Ruwan Gunesekara told Xinhua that one of the buses travelling from Aluthgama stopped at a bus terminal when another bus collided with it.
The injured included three women, Gunesekara said.
All those injured, including the 15 army soldiers, had been rushed to the Nagoda Hospital for treatment by residents in the area.
Police are conducting further investigations.