The 2015 Mustang GT has just been weighed by an actual owner for the first time on our forums.
Mustang6G member cj428 put his fully loaded 2015 Mustang GT Premium with Performance Pack on a scale and found that it weighs 3780 LBS.
Accounting for the 3/4 tank of fuel in his Mustang at the time, we see that a fully loaded GT Premium PP with no gas but all fluids weighs about 3700 LBS.
Read more about his impressions in the forum.