@lookitmychicken probably the quickest would be to google something like "kpop songs released in 2015" and skim through lists that come up. You can also use the generation the group debuted in to help. 2015 would be mostly 3rd Gen with some 2nd Gen.

Here's the generations chart by debut years that I use:

#1stGen 1992 - 2002
#2ndGen 2003 - 2012
#3rdGen 2013 - 2017
#4thGen 2018 - 2022
#5thGen 2023 - present