"He is thought to have tried to invest this money in a financial management firm in Geneva, but the establishment is believed to have refused for fear of future complications, Jérôme Cahuzac being a politically prominent figure," RTS said on its website, citing unidentified banking sources.
The sum was many times bigger than that evoked up to now in connection with Cahuzac, who was charged in France on Tuesday with tax evasion.
Cahuzac — who was responsible for cracking down on tax evasion while minister — finally admitted on Tuesday to having a foreign bank account after weeks of denials.
The 60-year-old announced his resignation on March 19th after prosecutors opened a probe into an overseas bank account, which held some 600,000 euros ($770,000).
On Saturday, the Zurich-based Tages Anzeiger newspaper said the politician had lied to a Swiss bank by asserting that funds paid into his account had been declared to French tax authorities.
After Switzerland agreed to conform to OECD rules on tax evasion in 2009, Cahuzac sought to keep the funds secret, closing his 600,000-euro account at Swiss UBS bank and transferring the money to Singapore to a branch of private
Swiss bank Julius Bär with the help of Geneva-based banking group Reyl & Cie.
The Geneva prosecutor's office which seized the bank documents concerning the account at UBS and Reyl said it had not looked into details of the account movements.
This should be done by Paris prosecutors who requested legal assistance in the case.
So far there has been no search at Julius Bär bank but prosecutors in Geneva have not ruled out that such a request will be made by Paris.
RTS television said "more substantial sums were deposited or transferred via Geneva in previous years", i.e before 2009.
The figure of 15 million euros mentioned in the RTS report corresponds to that given by Mediapart, the French online investigative journal, which broke the story.
Experts contacted by AFP would not rule out the existence of another account as the funds transferred to Singapore were relatively small given the fees charged for such transactions.
A French survey meanwhile showed that nearly two-thirds of French people are in favour of a government reshuffle following the tax fraud scandal.
Critics have rounded on President Francois Hollande — already in the doldrums in opinion polls.
"For the French, the Cahuzac affair is not an isolated act. There is mistrust towards their elected representatives," Frederic Dabi, deputy head of Ifop, the polling company that conducted the survey, was quoted as saying.