I agree with smaller meals more often. And even if she's 1500 grams right now, don't start pairing her yet. Keep feeding her until late fall. If you start pairing her now you might trigger a feeding fast. As long as she's eating just keep feeding her small to extra small rats more often. She will pack on more size in the next 2 months. It will benefit her greatly for breeding season.
1.400 gram is fine for breeding, but if she's not that old, she will probably not become gravid. Most bp's need to be around 3 years of age, before any good happens.
I asked the same question to a local breeder and was given the answer "who weighs these snakes in the wild?" So to his point an animal will breed sucessfully when its ready.