\(2\sqrt{15-\sqrt{216}}+\sqrt{33-12\sqrt{6}}\)
\(=2\sqrt{15-6\sqrt{6}}+\sqrt{33-12\sqrt{6}}\)
\(=2\sqrt{9-6\sqrt{6}+6}+\sqrt{24-12\sqrt{6}+9}\)
\(=2\sqrt{\left(3-\sqrt{6}\right)^2}+\sqrt{\left(2\sqrt{6}-3\right)^2}\)
\(=2\left|3-\sqrt{6}\right|+\left|2\sqrt{6}-3\right|\)
\(=6-2\sqrt{6}+2\sqrt{6}-3\)
\(=3\)