Inaccurate time and speed after saving (no sensors on bike)

During my rides, the speed and time is inaccurate.  When I save my ride, the time and speed are always too fast! I have been wearing my Garmin Fenix on ride function to compare, and the Fenix is correct.  For some reason, the Edge is calculating the speed and total time inaccurate.  For instance, I rode 15.92 miles (both Fenix and Edge recorded correct distance).  Edge stated I rode 20.5 mph avg speed in 46:30 time.  Fenix recorded 16.5 mph avg speed in 57:47 time (this was at a bike race, so I know my Fenix was correct). My Edge has been doing this since I purchased it a few months ago.  I just caught on that it was inaccurate.  I don't use any sensors on my bike and no E shifting either.  So annoyed!