Counter-terror officers rushed to Europe's busiest airport and stopped the plane, which was bound for Istanbul, the London Evening Standard newspaper reported.
They ordered the plane to turn around as it taxied down the runway.
The girl, from Tower Hamlets in east London, had secretly saved up to buy a ticket.
The incident happened earlier this month. The girl has returned to her family, the Standard reported.
"On December 6, police received reports of a 15-year-old girl from Tower Hamlets missing from home," a Scotland Yard spokesman said.
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"Police were able to locate her and she has since returned home safely."
Heathrow Airport declined to comment when contacted by AFP.
The Standard said the incident would heighten concern about the number of girls and young women travelling to Syria and Iraq.
An estimated 500 Britons have travelled abroad to become jihadists, many with the Islamic State jihadist group.
In August, Britain's terror threat level was raised to severe, the second-highest of five levels, meaning that a terror attack is considered highly likely.
It came against a backdrop of increasing concerns over aspiring British jihadists travelling to Iraq and Syria to learn terror "tradecraft".
Several teenagers are among those who have gone abroad to join fighters with Islamic State and other extremist groups.