Heritage Route 15, along with Heritage Route 9, was created in November 2005 by Transport for London to appeal to tourists and bus enthusiasts, retaining traditional Routemaster operation in central London. Operated by Stagecoach London, the Routemaster fleet was based at the former Waterden Road bus garage near Stratford until, in early 2008, it was demolished to make way for the 2012 London Olympic Stadium and Queen Elizabeth Park.
The fleet was subsequently moved to West Ham garage from where Heritage Route 15 ran between Trafalgar Square, Aldwych, Fleet Street, St Paul's Cathedral, Cannon Street and Tower Hill, overlapping with Heritage Route 9 along the Strand between Trafalgar Square and Aldwych. A fleet of ten buses operated the route (five buses running in service, with the other five as back-up), running between 09:30 and 18:30 daily and they were freshly painted into 1960s London Transport red livery with a cream relief band and gold London Transport fleet names and numbers.
A dedicated team of drivers and conductors crewed the fleet, dressed in period type uniform. Heritage Route 9 was dropped on 25 July, 2014, but in November 2015 TfL contracted Stagecoach to continue Heritage Route 15 until 2020 and it was planned for all ten vehicles used on the route to be refurbished internally and externally into almost original 1960s condition, complete with the correct dark red seat moquette and the reinstating of the original interior lighting. Only four out of the ten Routemasters, RM2060, RM1933, RM1941 and RM2089, were completed due to budgetary constraints and falling revenue on the route though.
Travelling between Tower Hill to St Paul's Cathedral the route is popular with tourists, but few make the whole end-to-end journey on Heritage Route 15 and so, from 1 March, 2019, weekday operation of the route was dropped in favour of working weekends and public holidays only between March and the end of September. ALM 50B (RM2050), entered service with London Transport at Aldenham Depot in October 1964, working Route 137.
In 1986 the vehicle was overhauled ready for transfer to London Transport's Commercial Operations (Sightseeing) unit, having an AEC engine fitted and reliveried into London Transport Red, with a cream band. Sold into preservation in 1987, RM2050 moved between owners until being completely rebuilt at Marshall (Cambridge) with a new engine, gearbox and interior improvements, after which it was allocated to Arriva London North for use on Route 38. In November 2005, RM2050 was removed from storage at Leyton and assigned to Stagecoach for use on Heritage Route 15, over which it still operates.