Three, four, or five scatter symbols will trigger 10, 14, or 20 spins, respectively. The cat symbol starts five positions high here, and will grow an extra one on every spin, raising the chances of landing it on the reels and therefore increasing your chances of triggering the Sweet 15 feature.
Retriggers are possible here, with 2, 3, 4, or 5 scatters adding 3, 5, 7, or 10 free spins, respectively.