Third Additional Metropolitan Sessions Judge Md Robiul Alam passed the verdict in the presence of the suspects on Wednesday.
This is the first time a Dhaka court has decided a case involving such a large consignment of drugs, according to state prosecutors.
They have each been fined Tk 10,000 in addition to the 15-year rigorous imprisonment. According to the case dossier, police detained a covered-van in front of a CNG filling station in Jatrabari's Kajla on Oct 17, 2016.
The law enforcers subsequently found 600,000 pieces of the methamphetamine-based drug with a market value of Tk 180 million.
Police later discovered that the consignment had arrived in the capital from Cox's Bazar's Teknaf and arrested four people in connection with the matter before starting the case.