The river of mud ploughed into a post occupied by 65 soldiers in the Rasuwa district, burying almost two dozen men alive instantaneously.
Five others were also feared dead on Sunday after heavy rains caused a mass of rock to cascade into Dhaibung village, 95km northwest of Kathmandu. All five missing are from the same family.
"After a day-long rescue operation with 150 soldiers, 15 bodies have been retrieved from the debris so far," said Army spokesman Deepak Gurung.
Heavy rainfall has caused extensive damage to the district’s infrastructure. Several roads and at least two bridges have been swept away, a home ministry source said.
Landslides are common in Nepal in summer when snow melts in the Himalayas and lowland areas are hit by monsoon rains and floods.
At least 147 people have died in landslides in Nepal since mid-June, according to Home Ministry figures.
Almost all the highways that link the Nepalese capital with the rest of the country have been closed at some points this summer by mudslides or landslides.
Around the same time last year, more than 40 people were killed when a village was destroyed by a landslide.