3 + 3 × [ 3 + 3 ÷ 3 × (3 + 3 × 3)] ÷ 15 =
3 + 3 × [ 3 + 3 ÷ 3 × (3 + 9)] ÷ 15 =
3 + 3 × (3 + 3 ÷ 3 × 12) ÷ 15 =
3 + 3 × (3 + 1 × 12) ÷ 15 =
3 + 3 × (3 + 12) ÷ 15 =
3 + 3 × 15 ÷ 15 =
3 + 45 ÷ 15 =
3 + 3 =
[tex]\boxed{\bold{6}}[/tex]