Some additional information:

You can stand (at 59, anyhow) right near the entrance inside of the Live side, and not get aggro from the first pull ofr level 55-56 skeletons. If you look forward, you can see where the wall for the gates stop and the hallway begins. This is where you want to be. Be careful about running too far ahead, because the gates for the entrance close down behind you, and the only way out is hearthing (or dying).

Be careful, because if you don't tag the mob immediately with the blaster when they're in range, they might walk out of range before the 2.5 seconds of channeling that's required elapses. You can stop some of them with /dance, but(!) they will not allow you to tag them with the blaster, while they're dancing, so it's kind of pointless.

The mob will run at you, and maybe get in a hit before it ""explodes"" into often one, but I've gotten up to four, wisps that are Restless Spirits.

These spirits will flicker around pretty wildly, and you have to tag them again with the blaster to get credit. The channeling effect will make it so that you will always be pointing at the spirit, so you don't have to manually try to keep it in front of you.

Timing from my chat log, the Spectral Citizens show up roughly 8-9 minutes apart, so assuming you only get one wisp per pull, that's 2 hours of sitting at the entrance. I managed to get all mine in just over an hour, though (one pull had 3, another had 4 wisps).

I misunderstood the quest and thought i just needed to zap the ghosts, thus i ran around the entire instance zapping most the ghosts i could find, but to my confusion after the run i still had 0/15.
I then zapped a ghostly citizen and then zapped the whisp(restless soul) - Score.
Since all the nice patrolling ghosts were zapped already i had to hunt for the ghostly ones - which only pop out of nowhere for about 30 sec before disappearing again.
I made this macro to ease the hunt a bit.<div class=""quote"">/tar Spectral
/tar Ghostly
/tar restless soul
/use Egan's BlasterIt work like a charm. It prioritizes restless souls &gt; ghostly citizens &gt; spectral citizens, so that if more is nearby and one is already zapped, you won't wast time zapping another and miss some souls(which despawn after a while)

Good hunting :)