Even though you could grep out the machines with open ports from this output, it would be quite a pain to parse everything with the multiline output. Instead, I used the -oG argument to nmap, which ...

nmap the 192.168.15.0/27 network for anything with port 161 open (some examples were dumb and looked for 162 as well- the trap port, we don't care about trap unless we are exploiting an SNMP vuln).