$=$ 2. Simplify the radical $\sqrt{2(6-2 \sqrt{3}-2 \sqrt{5}+\sqrt{15})}$.
$$
\text { 2. } \begin{aligned}
\text { Original expression } & =\sqrt{12-4 \sqrt{3}-4 \sqrt{5}+2 \sqrt{15}} \\
& =\sqrt{12-2 \sqrt{3 \times 4}-2 \sqrt{4 \times 5}+2 \sqrt{3 \times 5}} \\
& =\sqrt{(1 \overline{3}-\sqrt{4}+\sqrt{5})^{2}} \\
& =\sqrt{3}+\sqrt{5}-2 .
\end{aligned}
$$

Note: $12=(\sqrt{3})^{2}+(\sqrt{14})^{2}+(\sqrt{5})^{2}$.
