The suspected illegal immigrants were then detained on suspicion of illegal entry and escorted to hospital, where they will be given routine medical checks.
It was not clear whether or not the lorry had recently arrived in the UK via Calais. Police said the driver is assissting them with their enquiries.
In a statement Surrey Police said: “Officers attended the M25 Clackett Lane services at around 10.50am following reports of concern for safety.
“The driver of a white heavy articulated freezer lorry, who was travelling northbound, stopped at the service station after reporting he had heard loud banging coming from inside the vehicle.
“Fifteen people were discovered in the rear of the lorry.
“Surrey Police officers closed the main slip road into the petrol station while the people were detained on suspicion of illegal entry.
“Fourteen adults, along with one juvenile, will now be taken to hospital for medical checks following the incident.
“The driver of the lorry is currently assisting police with enquiries.
“The investigation will be passed to UK Visas and Immigration in due course.”