I can't recall the 4th location (Map) but it's PW, Mort, and Newland Desert is where I remember.
Newland desert I know the Nomads are lvl 30, the lowest QL armor type item I've looted I think was QL17, the highest QL41. Some did post a QL45 Cape but I cna not confirm if that was taken in Newland Desert or in one of the other 3 locations.
The Nomads have a bit of a slow attack, so not sure how your build is at lvl 15, but you may still want some help.
They do not drop Credits, like the RK Mobs do when you loot them, just the party stuff.
The Armor is NO DROP
In Newland Desert they spawn just about any where. Their spawn rate, well that is something, I had one spawn just as I started attacking another, then before I was finished with the first a third had spawned in the same spot.
And there are been times I felt like I ran for miles till I found another. But none of it is Bad, not in Newland Desert that is. I wanted to check out Mort, but my map Nav is not high enough to get that map. Running around Blind hunting these guys would be less fun (for me, others may enjoy it that way).
You could probably be able to solo the Nomads as a lvl 20, but that may depend of you knowledge of your class and armor/weapons. I would suggest getting in a Team. Team of lvl 15's could take care of themselves against the Nomads, at least a 3 player team , me thinks so
You could always tag along with a higher level, if you don't mind not gaining any EXP
Funny thing is I see a Nomad, go to attack and nothing happen, just to read the message PVP not allowed, LOL

. . what it was is a player wearing the Nomad armor, I wasn't paying attention to the target name, my eyes was on the body
I just hope more are looking for parts this time when I log in, last night I never got a chance.