Is that really the question you want to ask, or do you want to know what the process is?
515 seems to be a "spooler" (printer) according to IANA. So if you are running some printer software, you can try to stop it or if you can configure it properly it should be run on the loopback.
You could also try using a firewall, which is almost a necessity these days anyhow.
EDIT: You can also try
fport to see the process using that port (never used it, and never used ME so it may not work there

).
There might be a netstat flag to show the process in use too, although this may be only XP's netstat.