V.T172 — Primary Baryogenesis Formula: η_B = α·ι_τ¹⁵·(5/6)

η_B = α·ι_τ¹⁵·(5/6) = (121/270)·ι_τ¹⁹ ≈ 6.041 × 10⁻¹⁰ at −1.03% (−10320 ppm, −1.09σ) from Planck 2018 value 6.104 × 10⁻¹⁰. Scope upgraded from conjectural (V.R324) to τ-effective based on: (1) structural derivation of exponent 15 = dim(τ³)×|generators| = 3×5 (V.T170), (2) (5/6) shared threshold-counting coefficient with Y_p (V.T171), (3) Majorana neutrinos (IV.T146) structurally enabling L→B conversion, (4) unique minimum in 77-candidate exponent scan (k=10..20, 7 coefficient families).