It’s possible you have the old MPQ era updater programs in your wow folder. Their naming sequence is essentially wow dash buildnumber to buildnumber.exe or just buildnumber.exe
IMHO the best option is to grab a file tree size utility like Jam Software’s Treesize Free and point that at your Wow folder.
Anything that’s in the Data folder and the client programs like wow-64.exe are essential so don’t delete those.
I concur with Assabelora, it sounds like WoW might have missed a chance to reclaim disk space on an update somewhere, my install is only 73 gigs. There might be an update patch that didn’t get deleted or something along those lines.
I agree with Tofflemire here. There should not be a second World of Warcraft sub-folder located inside the main World of Warcraft folder. That kind of sounds like the game somehow got reinstalled inside the main folder, so you effectively have two installs of the game.
You can safely delete that sub folder, so you only have _retail_ and Data folders remaining, along with the other files in there.