Aljazeera reported on Wednesday that civil defence and rescue workers had pulled out a total of 15 bodies from the rubble.
The building had on Tuesday collapsed on an adjacent primary school's wall, killing a seven-year-old child.
Police said on Wednesday the toll from the accident rose from a previous tally of 12 after four more bodies were retrieved from the site.
Several people were still trapped under the rubble of the six-storey building and rescue teams were looking for survivors, with relatives gathered around the site, police said.
A five-year-old boy and a woman were rescued on Wednesday.
The building in a residential neighbourhood of eastern Alexandria was originally three floors high but another three floors were added illegally.
Building collapses are a frequent occurrence in Egypt.
Many structures are unauthorised and not built according to regulations.