Time period of spring $=2 \pi \sqrt{\frac{k}{m}}$

Time period of pendulum $=2 \pi \sqrt{\frac{l}{g}}$

Time period of spring will not be affected by gravitational acceleration.

Let mass of earth be $m$

Mass of new planet $=\rho \times \frac{4}{3} \pi(2 R)^3=8 m$

$g_2=\frac{G M_2}{\left(R_2\right)^2}=\frac{G \times 8 M}{(2 R)^2}=2 g$

$T_2=2 \pi \sqrt{\frac{I}{2 g}}$

$T_2=\frac{T}{\sqrt{2}}$

Hence $P$ will move faster.