#!/bin/bash
s='1.15.2.119
1.15.86.33
1.15.251.60
1.20.178.145/31
1.37.33.24
1.54.202.216
1.58.10.126/28
1.80.225.84
1.116.240.174/30'

sed  '\,/,!s,$,/32,' <<< "$s"