Heterodimer of A and B chains; disulfide-linked. Expressed by the venom gland. The presence of a 'disulfide through disulfide knot' structurally defines this protein as a knottin. Contains 4 disulfide bonds. Belongs to the neurotoxin 19 (CSTX) family. 12 subfamily. It is probable that CSTX-15 A and B chains originate from the same gene. Both chains may be separated by some amino acids. May be a cleavage product of CSTX-13.