An operating system used Shortest Remaining System Time first (SRT) process scheduling algorithm. Consider the arrival times and execution times for the following processes:$$\small \begin{array}{|c|c|c|} \hline \textbf{Process} & \textbf{Execution Time} & \textbf{Arrival Time} \\\hline \text{P1} & 20 & 0 \\ \text{P2} & 25 & 15 \\ \text{P3} & 10 & 30 \\ \text{P4} & 15 & 45 \\\hline \end{array}$$What is the total waiting time for process $P2$ ?
- $5$
- $15$
- $40$
- $55$