Across the city 1,826 patients were treated by the charity, with more than a third of the casualties resulting from road traffic collisions.
The Air Ambulance had no explanation of why, for the third year running, Westminster needed the service most.
Lambeth, with 113 call-outs, and Hackney, 111, made up the top three.
Westminster had the highest number of call-outs the two previous years as well, figures show, with 120 patients in the borough treated in 2014 and 141 in 2013.
1,826
patients treated
Busiest boroughs Westminster: 115, Lambeth: 113, Hackney: 111
Injury types 601 road traffic cases, 528 stabbings and shootings, 433 falls, 264 others
In January, the charity's second helicopter carrying an advance trauma team became operational.
Graham Hodgkin, chief executive officer of London's Air Ambulance, said: "While our statistics show that we were busier in some areas of the capital than others, trauma can happen to anyone, anywhere, at any time.
"There could be any number of reasons for why we might be busier in one area over another, including weather, density of population or high profile events - there really are no trends for this particular disease.
"Now with two helicopters to maintain, and the extension of our daylight flying hours in the summer months, the cost of providing our service to London has increased to Â£6m each year."
Dave Cowe was treated by an air ambulance crew last September when he came off his motorcycle and landed on the concrete.
Most of his ribs were fractured, his head injured and his left lung was at risk of collapsing with his chest filling up with blood.
Mr Cowe said: "I was very lucky. London's Air Ambulance was by my side in minutes delivering what is essentially a mobile emergency unit with a doctor on board.
"It's crazy to consider that until recently London only had one helicopter."
Barts Health NHS Trust provides the doctors while London Ambulance Service provides the paramedics and emergency kits.
Top 10 busiest boroughs
London's Air Ambulance crews attended 115 incidents in Westminster last year, the highest number of call-outs in any of the capital's boroughs.