The Heathrow Express from Paddington reaches the airport in approximately 15 mins

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 about 15 mins. It’s the fastest rail selection, regardless that pricier than the Tube.