The Heathrow Express from Paddington reaches the airport in about 15 minutes

https://www.scribd.com/document/1074929924/National-Rail-to-Heathrow-Routes-Transfers-and-Tickets-Explained-232993

The Heathrow Express from Paddington reaches the airport in approximately 15 minutes. It’s the quickest rail selection, although pricier than the Tube.