IFF the aircraft rolled off the production line 1.5 tonnes lighter, that is not good management, that is luck.
Not really - while there is certainly some variability in the airframe weights between line numbers, it's no where near 1.5 tons on a 787. Rather, the 787 has benefited from aggressive weight reduction programs, such that
all current production 787s are similarly 'underweight'.
Current production 747-8F are over 5 tons light than the early production, there has been a similar % improvement on the 787 (especially compared to the first ~20 aircraft which were badly overweight).