The teenager was set upon by a group of youths in Linwood Road, in Handsworth, at around 3.30pm on Thursday.
He was rushed to hospital but died from his injuries a short time later.
Witnesses say shots were heard and the suspects were armed with knives. The suspects are believed to have fled in a white car, which later crashed into a house a short distance away in Wheeler Street.
No arrests have been made.
Detective Chief Inspector Alastair Orencas, from West Midlands Police's homicide team, 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."
A West Midlands Ambulance Service spokesman said: "We received a number of calls to Linwood Road in Handsworth, Birmingham at 3.39pm on Thursday afternoon.
"Three ambulances, a paramedic officer, a critical care paramedic and a BASICS emergency doctor attended and arrived on scene to find a male requiring emergency treatment.
"Ambulance crews provided advanced trauma care on scene before conveying him to hospital on blue lights, where he later sadly passed away.”
On Thursday night the road was closed with a cordon in place around the scene. The car is being examined for forensic evidence and officers are speaking to witnesses and checking CCTV in the area.
Anyone who witnessed what happened and has not spoken to police is urged to call 101. Alternatively, witnesses can call Crimestoppers anonymously on 0800 555111.