Health officials say they are all linked to previously reported cases and 11 were in quarantine during their entire infectious period. The state now has 163 active cases.
Victoria administered 29,490 vaccine doses in the 24 hours to Friday evening and conducted 33,675 tests for the virus during the same period.
Meanwhile, Australia's biggest mall, Chadstone shopping centre in Melbourne, has been declared a COVID-19 exposure site.
The centre was declared a tier two site on Friday night.
Anyone who was at Chadstone between 4.26pm and 5.40pm on Saturday August 7 must take a COVID test and isolate until they receive a negative result.
The Coles supermarket within the shopping centre has also been listed.
There are now more than 450 exposure sites in Melbourne including Highpoint shopping centre and several large apartment blocks.
Meanwhile, Victoria's Chief Health Officer Brett Sutton says the lockdown's ongoing toll on children is "heartbreaking", as mystery Covid-19 cases threaten to further extend the shutdown.
Professor Sutton said he considers the social impacts of lockdowns when providing health advice to the state government, including keeping children out of school and away from their friends.
"It's heartbreaking," he told 3AW of having to explain that fact to his own three young children.
"But, again, what alternative pathway have we got available to us? Because we know what happens when restrictions are not done in a timely way or are not sufficient to control transmission - it explodes in numbers."
Melbourne is into the second week of its sixth lockdown, brought on to contain several Delta variant outbreaks.
But contact tracers are racing to discover the source of concerning mystery cases, with 13 emerging in the past three days.
Of the 15 locally acquired coronavirus cases reported on Friday, the origin of four was under investigation and seven were out in the community while infectious.
Professor Adrian Esterman, an epidemiologist and biostatistician at the University of South Australia, believes Melbourne will get on top of its Delta variant outbreaks, but not by August 19 when the lockdown is due to end.
"I would say it's highly unlikely," he told AAP.
"I don't think that lockdown will finish ... until you're in single digits and have no mystery cases."
Unexpected wastewater detections have also arisen in the regional areas of Shepparton and Lakes Entrance, where there are no known active cases or current exposure sites.
Professor Sutton expects the list will grow over the coming 24 hours.
The Victorian government has set an ambitious target of one million Covid-19 vaccine doses in five weeks, and will open up access to the AstraZeneca vaccine at all 50 state vaccination hubs to help reach the goal.
