The ambush took place in Semdinli in Hakkari province, along the borders with Iraq and Iran.
The Turkish military regularly carryies out air assaults on PKK bases across the border in Iraq.
Turkey's foreign ministry urged Iraq to "take the necessary precautions and prevent the repetition of such attacks". Iraq condemned the attack but called on Turkey to act with "wisdom and self-restraint".
Halidun Zomazturk, a retired Turkish brigadier-general, told Al Jazeera: "At last the government is taking this very seriously."
Turkey's military said its soldiers opened fire in response to the attack on the outpost. At least 20 Turkish soldiers were also wounded in the fighting.
General Metin Gurak, who heads the Turkish general staff's press department, told the Anatolia news agency that two soliders remained unaccounted for.
He said that Turkish forces had used artillery fire and attack helicopters, while additional forces had been dispatched to the area.
"Most of our losses were caused by heavy weapons' fire from the north of Iraq," Gurak said.
Turkish fighter jets and artillery units also attacked a group of PKK fighters in the north of Iraq, about 10km from the station, Gurak said.
Yousef al-Sharif, reporting for Al Jazeera from Ankara, the Turkish capital, said a military operation was under way in the area as a result of the attack.
"You can say that Turkey was shocked today by the news [of the soldiers' deaths]because nobody was expecting such a big attack from the PKK - 15 soldiers is a big number now in Turkey," he said.
The PKK, based in south Turkey and north Iraq, has been fighting for autonomy for more than two decades.
Ankara blames the PKK for the deaths of more than 40,000 people since it launched its campaign for an ethnic Kurdish homeland in 1984.
Tayyip Erdogan, the Turkish prime minister, asked parliament last month to extend a mandate, which expires later this month, to launch further military operations against the PKK in Iraq.