Using your term, the impostors are usually not going to line up perfectly with the real deal. The first thing to do is to check the existing listings. For coins over 20 years old, there are not many unknown significant doubled dies and RPM. They do exist, for sure, but the odds of finding them over a small run of coins is very small. If you have something that does not match an existing listing, that's a first clue. In your case, there are probably many uncataloged Class 9 doubled dies from that era, since 2015 is recent and the pop doubles are quite numerous.
The second clue is whether or not the doubling has characteristics of
Machine Doubling or
Die Deterioration Doubling. Certain types of true doubling do present similar to MD. The 1942 type 1 nickel FS-101 is a good example of something that looks similar to MD. The extra thickness double types from distended hub doubles can also look like
DDD. For your coin specifically, the Class 9 jolted doubles can look similar to MD.
From there, you get into the technical nitty gritty of how to analyze a doubled die, as laid out by Dr. Coop, Mike Diamond, and other experts.