The 14 men and one woman, all from Syria, were discovered shortly before 5am at the Port of Calais on 6 June when Border Force officers, along with sniffer dog Ronnie, searched the Bulgarian registered lorry as it waited to board a ferry to the UK.
The truck was carrying a load of mouthwash.
The stowaways were handed over to the French border police and the vehicle was allowed to continue on to its destination.
Paul Morgan, Border Force Director for South East & Europe, said:
“This incident shows why we base Border Force staff in France – to stop would-be illegal immigrants before they can reach the UK.
“Our strong presence in French ports like Calais and close collaboration with the French authorities helps protect the whole of the UK from people attempting to enter the country illegally.
“As well as using sniffer dogs, officers also use heartbeat detectors, carbon dioxide probes and physical searches to find people hiding in vehicles”.