Two men died at Mayo Hospital in Lahore while 13 had died yesterday, officials said. Five more men were being treated in hospital.
According to police, most of the victims were drug addicts aged between 15 and 35 years who had been drinking cough syrup to get intoxicated.
Police raided several medical stores and pharmacies in Lahore to confiscate stocks of "Tyno cough syrup".
They also sealed the factory that makes the syrup and arrested its owner.
Khwaja Salman Rafiq, health adviser to the Punjab government, too confirmed 15 deaths.
He said stocks of Tyno syrup had been confiscated from all medical stores and pharmacies.
The factory manufacturing the syrup was sealed and samples sent to a laboratory for analysis.
"Initial reports suggest that the victims had consumed expired and excessive doses of the syrup," he said.
Over 20 men fell ill or fainted after drinking the cough syrup in the thickly populated Shahdra Town neighbourhood of Lahore yesterday.
Several stores were selling the cough syrup for Rs 25 to Rs 40 a bottle, officials said.