A military statement said the bomb also wounded 25 people, including 15 civilians.
An emergency has been declared in the city following the incident.
Pakistan's army press wing said the patrol was the target and there were at least seven civilians among the 15 killed.
ISPR Director General Major General Asif Ghafoor said in a Twitter post that Chief of the Army Staff has condemned the attack and termed it an attempt to mar the Independence Day Celebrations. "At least 32 others are wounded", Balochistan home minister Sarfraz Bugti told AFP, adding that a rescue operation was still underway.
Security officials said the explosion set on fire multiple vehicles at Pishin Stop in the provincial capital of Balochistan.
Middle East-based Islamic State, which has a branch of loosely affiliated fighters in Afghanistan and Pakistan, claimed the attack shortly afterwards, saying a motorcycle suicide bomber had killed 17 soldiers. "Our resolve won't succumb to any challenge", Maj Gen Asif Ghafoor tweeted.
Mineral-rich Balochistan, where Gwader is located, has been plagued for decades by a separatist insurgency and sectarian killings.
Security forces cordoned off the blast site for investigations.
The province has also seen a number of attacks carried out by the Lashkar-e-Jhangvi's Al Alami faction, a group with ties to ISIL, known for attacking Shia Muslims.
A judicial report released after an attack on the province's lawyers left more than 70 dead criticized security provisions in the region and called for increased clampdowns on extremists.