Some information would be helpful.
Why is Lightroom creating a new previews folder?
How much RAM?
How much free disk space?
Any other details that can give us an idea of what you are doing.
I Have a canon 5 D MIII, USING YOSEMITE OS. I HAVE NO CLUE WHY ITS CREATING THIS FOLDER, IM TRYING TO FIGURE THAT OUT!!!
im simply doing a standard import from the memory card and this happens! Not every time, but it's becoming more frequent
Lightroom will build previews when you are looking at the files in library when they are needed if you do not build them when you first import. If you want just the embeded previews and not have previews built at import then set the following in the import dialog. This will slow you down later on when you are scanning the library as previews are needed and they are not prebuilt. Get used to the preview files as they are unavoidable.
Build Previews Minimal
Uncheck Build smart Previews
I thought you were saying that Lightroom was stuck building a previews folder. Lightroom generates a preview for every image that you import. This preview displays the changes you make to your images. You have to have a previews folder because it's part of the Lightroom workflow.
What OS? How much RAM? How much free disk space? Answers to these types of questions might enable someone to give you some ideas of what to do.