Kgosientso Ramokgopa said at a press briefing that the city's audit unit had been carrying out investigations and that disciplinary action would be taken against the 15.
He did not reveal the nature of the offences, but last week President Jacob Zuma signed proclamations authorising the Special Investigating Unit (SIU) to investigate concerns around procurement, as well as allegations of mismanagement and maladministration at the Tshwane Metropolitan Municipality.
Ramokgopa, who replaced his aunt as mayor, said: "The city has been working on the issues that the SIU will be investigating. Most of these issues are those that have been raised by the auditor general in some of the reports and interactions that we have had with them. To this end we view and welcome the SIU investigation as a timely intervention."
He said that the city had pledged to contribute toward the costs of the investigation "to demonstrate our commitment to the investigation".
The investigation is expected to last 24 months.
"We plead with all stakeholders to allow the SIU to conduct the investigation without any interference, undue influence and limitation of scope. Our attitude towards any investigation is that a determination must be made as to the correctness and veracity of the allegations on the table, without any assumption of wrongdoing," he said.
The Pretoria News reported on Monday that a Lead SA poll had revealed that after Johannesburg and Ekurhuleni, Tshwane metro cops were next in line for demanding bribes.
According to the poll that was conducted over a period of two days, 2 474 people admitted to paying a bribe to metro cops.
Most of the bribes were paid in Johannesburg, with 1 889 incidents reported, followed by Ekurhuleni with 387 and Tshwane with 121.
Capetonians seemed to be the most law-abiding citizens with only nine people admitting to bribing officers.
The Pretoria News recently reported that 25%t of the Tshwane metro police force members were under investigation.