The roots of polynomial $ p(z) $ are:
$$ \begin{aligned}z_1 &= 1.4142+1.4142i\\[1 em]z_2 &= 1.4142-1.4142i\\[1 em]z_3 &= -1.4142+1.4142i\\[1 em]z_4 &= -1.4142-1.4142i \end{aligned} $$Polynomial $ z^4+16 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.