I don't own any giants but I hope I can give some grounded general advice.

First take a step back and look at why your wanting a "Big" snake. I think that if you have the ability and space to properly house and care for the animal good. Is it because you just want a "big" snake or do you really enjoy the species. If its the first reason get rid of it! Its a danger to the snake first hand foremost then you and others when kept for that reason. If you really enjoy the species start with a hatchling not a 6'-8' animal people that buy those size animals are one of two people (people that are or were giant owners or people that only want a "big" snake and don't wont to "wait 3 years for it to get that big). Just remember that Zoo's and pet stores do not take 15'+ snakes cause you can no longer feed and house it.

Second while your husbandry may be spot on are all of its requirements being met? Security is a big factor with all snakes. make sure that your offering it an environment that is both secure and keeper friendly.