For a series RLC circuit, charge at time \(t\) is given as \(q(t)=Q e^{-R t / 2 L} \cos \left(\omega^{\prime} t+\phi\right)\), where \(Q\) is the amplitude at time \(t=0\). If \(R=2 \Omega, C=2.3 \mu \mathrm{F}\) and \(L=15 \mathrm{mH}\), find the time at which the amplitude of the charge oscillations in the circuit will be \(70 \%\) of its initial value.