Witnesses described hearing gunshots and the suspects were armed with knives. It happened in Linwood Road in the Handsworth area of the city just after 3.30pm on Thursday.
The teenager was taken to hospital but died from his injuries a short time later, West Midlands Police said.
The suspects fled in a white car which crashed into a house a short distance away in Wheeler Street, the force added.
No arrests have been made.
Detective Chief Inspector Alastair Orencas, from the homicide team, who is leading the inquiry, said: “This level of violence in broad daylight on a residential street is inconceivable, let alone the fact that the target was a 15-year-old boy.
“We are leaving no stone unturned in our search for those responsible and I ask anyone who knows who they are to contact us.
“The family of the boy has had the worst shock imaginable today and we have specialist officers with them in their time of grief.”
