\[3x^{3} - 5x^{2} + 2x - 15;\]
\[x = 2x^{2}:\]
\[3 \cdot \left( 2x^{2} \right)^{3} - 5 \cdot \left( 2x^{2} \right)^{2} + 2 \cdot 2x^{2} - 15 =\]
\[= 3 \cdot 8x^{6} - 5 \cdot 4x^{4} + 2 \cdot 2x^{2} - 15 =\]
\[= 24x^{6} - 20x^{4} + 4x^{2} - 15.\]