Fourteen cases of malaria have also been recorded till May 26, with 10 of them this month.
Of the 15 cases of dengue, six were recorded in January, three in February, one in March, two in April and three this month, according to the report.
The cases of vector-borne diseases are usually reported between mid-July and November-end, but this period may stretch up to mid-December.
There were no cases of any vector-borne disease till January 13.
Meanwhile, domestic breeding checkers have found mosquito-breeding at 19,205 households in the city till May 26, the report said.
"24,084 legal notices have been served for mosquito-genic conditions and 1,730 prosecutions have been initiated," it said.
South Delhi Municipal Corporation (SDMC) Commissioner P K Goel had last month issued an advisory on prevention and control of vector-borne diseases in Delhi.
He had urged the heads of educational institutions and offices to cooperate in checking mosquito breeding in their areas.
He also asked heads of various offices to nominate nodal officer to ensure compliance with advisory and proper prevention.
At least 10 people died in Delhi due to dengue last year, according to the SDMC, which tabulates data for the entire city. Five of the 10 victims were not Delhi residents, but had died in the national capital.
Overall, the vector-borne disease had affected 9,271 people in the city in 2017.
The official toll maintained by the Delhi municipal authorities till December 26 had stood at four, even though some hospitals had reported a few more deaths due to dengue.
The mosquito-borne tropical disease had claimed its first victim in the city last year on August 1, when a 12-year-old boy died of dengue shock syndrome at the Sir Ganga Ram Hospital (SGRH).
Three more deaths were reported in October by the SDMC.
The numbers of malaria and chikungunya cases recorded in 2017 stood at 1,142 and 940, respectively.