Let \( z_1 \) and \( z_2 \) be two complex numbers such that \( z_1+z_2=5 \) and \( z_1^3+z_2^3=20+15i \). Then, \( \left|z_1^4+z_2^4\right| \) equals:
\( 25\sqrt{3} \)
\( 75 \)
\( 15\sqrt{15} \)
\( 30\sqrt{3} \)