You should delete the files manually—the contents of the two folders under: C:\Users\yourusername\AppData\Local\Adobe\Lightroom\Caches\Video
LR goes crazy you click on an Import folder as you’re navigating down to it. Whenever you click on a folder it tells a separate executable called DynamicLinkMediaServer.exe to index ALL the video files starting with whatever folder you click on to open the folders to navigate to where you’re importing from. There could be many videos on whatever drives you import from and all of them will be indexed if you click on the drive letter to start navigating to where you want to import from. That’s the problem. LR is crazy in telling the DLMS to index everything instead of just where you finally import from.
LR uses the same place to store its video cache when you’re actually working on a video you’ve imported, but it doesn’t know about the other files in there and doesn’t delete them.
thanks a lot! thats helpful to know. would you suggest i no longer import video files to lightroom then?
You don't have to import anything to have the problem so not importing videos won't help.
In LR 5 if you just click on the folder arrow on the way to getting to your photos (not even videos) deep down, then the DynamicLinkMediaServer is told to index the entire subfolder structure that is below the arrows you've clicked to get to the folder you want to import from.
In LR 6/CC 2015 it seems to be only videos that show up in the grid before you click Import so not from every folder that you've clicked on.
Besides deleting the cache folders, I'd suggest creating a shortcut to the Video parent folder on your desktop or somewhere else easy to get to so you can go there periodically to delete what's built up in there, since the last time. Until Adobe fixes LR to not index more than needed the cache folder will continue to get filled with extra cache files every time you import.