A 1300g male eating a 100g rat will be fine for a while. I personally wouldn't feed him again right now, but my males aren't even on the food rotation for me...they just get the semi-irregular uneaten meal. Even averaging less than a weaned rat (45g) a week they do fine.
The 15% general rule is only for hatchlings and smaller BP's. You definitely do not need to feed adult BPs 15% of their bodyweight.