The incident happened in Nguetchewe village in Cameroon's far north region, near the country's border with Nigeria, and was carried out by suspected Boko Haram militants, the official said.
The militants crossed from neighboring Nigeria around midnight and stormed an IDP camp, throwing a grenade in a group,killing 13 people instantly, according to Medjeweh Boukar, an army major.
"13 persons died on the spot and two died in the hospital and my convoy is now taking the bodies to the village," Major Boukar told CNN after the incident.
Major Boukar said Cameroon's soldiers are investigating the attack.
Boko Haram, originally from Nigeria, has been mounting attacks in Cameroon, Chad and Niger.
The jihadist organization and its splinter group, the ISIS-aligned Islamic State West African Province (ISWAP), have caused violence and destruction in Nigeria's northeast and the surrounding Sahel region over the last decade.
The government of Nigeria declared Boko Haram a terrorist organization in 2013, and several months later, the US State Department followed suit.