USGI and Korean
Note on the Korean
The vast majority of the ones marked & marketed as Korean military surplus are not
They are Korean commercial made, just packaged and sold to appear as surplus
So do not spend extra thinking you are getting something extra
You specified 15 rounders but I'll throw out some info on the 30's as inevitably someone will ask about them. The vast majority (>99%) of 30's found out there are commercial copies (even if marketed/marked as GI) and are junk, don't waste your money. Sure you might luck out and eventually find one that works decent, but you'll likely have spent a bunch of money on junk ones to find the one good one.
USGI 30's came in two types, hardback and splitback
The splitback was the most produced and the most copied
In my experience there is at least a 20:1 ratio of commercial copies to actual USGI 30
It takes a bit of knowledge and experience to identify the real ones, but once you figure it out IDing them is easy. Unfortunately the nice USGI's get snapped up fast or are beat up pretty bad and often not worth buying.
There is one easy way to avoid the above mess if you want a functional 30, buy a hardback
They were the least produced because they were difficult and costly to make, which is why no one ever tried to make a commercial version of them. So when you find one you its the real thing and you know it will work (if not damaged) and they do work outstandingly well
The bad part is they are rare and costly
New in wrap ones would typically set you back $200
The good news is that a small batch of them were found NIW in Europe not long ago, so prices were driven down under $100. But that batch is about gone and prices are climbing again, so buy soon.
You might think that it's nuts, but they are the best mags ever made for the Carbine. And look at it this way, I've seen people spend $20ea on a half dozen 30's only to get just one that 'sort of worked' most of the time. When they could have just bit the bullet and bought a hardback for what they spent on the junk. With a bonus being that the hardbacks hold their value.
Good luck
