I would not use V15 unless it is for colubrids, not worth the price considering that a BP would not stay in there for very long and would need to be transitioned to something bigger pretty fast.
I use V18 for holdback hatchlings (from out of the egg to 600 grams), after that they go directly in their adult racks.
As for what to get well it depends on what you need, have you started breeding, do you have hatchlings due or do you have animals needing an upgrade? Keep in mind that once your first female ovulates you sill have roughly 100 days before having to house your hatchlings.