The suspects were taken from the vehicle in Hinckley Road, near Leicester Forest East and were handed over to immigration officials for their status to be checked.
A Leicestershire Police spokeswoman told local media:
“Police received a call at 2.38pm from a member of the public who raised suspicions about a lorry travelling in the Lubbesthorpe Way area.
“The vehicle was stopped by police officers at Desford Crossroads and 15 people were detained on suspicion of illegal entry into the UK.
“The immigration service were informed and are now dealing with checking the status of the people detained.”