The roots of polynomial $ p(x) $ are:
$$ \begin{aligned}x_1 &= 0.2176\\[1 em]x_2 &= 0.6951\\[1 em]x_3 &= -0.4563+0.8207i\\[1 em]x_4 &= -0.4563-0.8207i \end{aligned} $$Polynomial $ 15x^4+3x^2-10x+2 $ has no rational roots that can be found using Rational Root Test, so the roots were found using quartic formulas.