UK officials have vowed that tackling people smuggling remains a priority after arrests were made in connection with the deaths of 27 people trying to cross the English Channel in a dinghy last winter.
The National Crime Agency (NCA) said it had worked with a French border police unit which targets immigration crime to provide evidence to identify the 15 people arrested.
The suspects were detained across locations in France last week in relation to the November tragedy, in which victims died when the boat they were in sank off the coast of Calais.
Five people were arrested in France soon after the incident.
Among the 15 people arrested last week by the French border police unit known as Ocriest were Afghan, Pakistani, Iraqi and French nationals.
Those arrested are suspected of being part of a network of facilitators who organised places on the boat for a number of those who died, the NCA said.
They are all expected to be subject to judicial proceedings in France.
Andrea Wilson, NCA deputy director of organised immigration crime, said: “The events of last November were a tragedy, but in that time our resolve to bring those responsible for these deaths to justice has not diminished.
“We have worked closely with our French partners to identify those who we suspect were involved, and that joint investigation continues. It is also assisted by Border Force and Maritime and Coast Guard Agency in the UK.
“Many of those involved in organising these dangerous crossings operate outside the UK, so it is vital we work closely with law enforcement partners in France and beyond to target them.
“This includes having NCA officers based overseas, sharing intelligence and working side by side on joint investigations, as we have done in this case.
“Tackling people smuggling remains a priority for the NCA.”
Home Secretary Priti Patel pledged to “crack down on the evil people smugglers”.
She said: “My thoughts continue to be with the families of all of those who tragically lost their lives in this horrific incident.
“The NCA and other agencies across the UK and France will continue their tireless work to deliver justice for the victims and their families by identifying those responsible and ensuring they feel the full force of the law.
“By working together, and through the tough new domestic measures we have just brought into law, we will crack down on the evil people smugglers in our efforts to prevent any more loss of life in the Channel.”
A recent PA news agency analysis of Government figures showed that more than 3,000 migrants crossed the Channel to the UK in June – the highest monthly total this year.
Some 3,136 made the crossing on 76 boats in the 30-day period, with journeys taking place on 19 of those days.