Eren Bulbul died from wounds sustained as he helped gendarmes track PKK terrorists in Macka, a town 22 kilometers (14 miles) south of the Black Sea province of Trabzon.
Gendarmerie Master Sgt. Ferhat Gedik, 41, was injured in the same incident and also martyred.
Funeral prayers for Eren was held Saturday afternoon and was attended by Interior Minister Suleyman Soylu.
Deputy Prime Minister Fikri Isik visited the hospital where Eren had been treated to express his condolences to the boy’s family.
Kemal Kilicdaroglu, head of the opposition Republican People’s Party (CHP), condemned the attack.
“You are so low as to fire a bullet at a 15-year-old boy,” he said in a tweet.
Kilicdaroglu also called Eren's brother Olcay on Saturday and expressed his condolences, according to a statement made by CHP on Saturday.
Many people in Macka reacted to the killing of Eren by hanging Turkish flags at their houses and workplaces.
A poster of Eren was also hung outside the town hall with the words “Eren Bulbul, Macka will never forget you. Our martyrs rest in peace.”
On Twitter, thousands of Turkish people posted messages commemorating Eren with the hashtag #iyikivarsınEren (means 'glad to have you' in Turkish).
NGOs, artists, businessmen and sport clubs all over Turkey condemned terror and killing of the 15-year-old boy, in statements.
Football teams in the Turkish Super Lig will also come out onto the pitch with banners commemorating Eren and will stand in silence for one minute during the first week of the league on Saturday, Sunday and Monday, according to a statement of Turkish Football Federation on Saturday.
The PKK -- listed as a terrorist organization by Turkey, the U.S. and EU -- resumed its armed campaign against Turkey in July 2015.
Since then, it has been responsible for the deaths of some 1,200 Turkish security personnel and civilians, including women and children.