How long would a flight from Philadelphia to Egypt take?

A random search for flights from Philadelphia (PHL) to Nairobi (NBO) shows:

OPTION 1: 18hr 40min via London Heathrow (LHR)

PHL - LHR British Airways Flt 66 Dep 06:55pm 18Dec,Fri
LHR - NBO British Airways Flt 65 Dep 10:05am 19Dec,Sat
Flight Duration: 15hr 25min; Layover Time: 3hr 15min; Total Trip Time: 18hr 40min