Extremely long flight times (on VS41)

I'm flying to SFO on VS41 next Saturday and I have a habit of looking at what recent flight times and schedules were like I took a look and most flights were between 10.5 and 11.5 hours like normal. But I was surprised to see that VS41 on May 8 left almost on time but landed almost four hours late with a flight time of almost 15 hours

So I was just intrigued, is the likely reason for this strong headwinds, a tech issue, or..? And perhaps just to keep it more interesting, if anyone else has experienced extremely long flight times compared to the usual?

Fingers crossed I'm closer to the official 11 hours next weekend

That time is going to include any delays at the origin, in this case Heathrow. FR24 lists a flight time on the 8th of 10 hours32 although it didn't take off until 20:39.
I'm guessing there was some delay after original pushback hence the "extra" four hours.

Ahh you're right. I looked at a more detailed page and while pushback was roughly on time, actual takeoff was four hours later. Ouch!

I am now kinda intrigued just how much longer an actual in-flight run can take under the worst flight conditions though.

We had exactly that. LHR-SFO in April 22 on "Penny Lane"
Departed the gate exactly on time around 12.30pm. Flight time was advised as 10 hours 20 minutes.
Half way to 27L the aircraft stopped and after about 15 minutes the Captain dvised that there was a small issue with an engine and it would take around 30 minutes to restart.
45 minutes later, Captain advised returning to stand as needed engineers.
After another 2 hours of sitting on the plane Captain said that aircraft was unservicable and luckily another 787 was available with same config, so it was deplaining Penny Lane and bussed to 2nd aircraft which was other side of T3.
This was just after covid where a 24 hour pre test needed to be done. Crew were almost going to be out of hours but they worked as fast as possible to transfer everyone with only 1 bus.
Took off almost 5 hours late and arrived into SFO 4.5 hours late.
Was happy to get there and that VS did their best not to cancel the flight.
Applied and received the UK261 within 14 days.