Yes you can Delete the Previews, the folders under the top level Lightroom 5 Catalog Previews.
You can do that anytime you like and LR will rebuild the previews as you view images. But having the Previews allotted size set to only 2GB is going to cause you some problems. Set it to 20GB.
Thanks for your quick response!
Just to be clear, my preview cache is not limited to 2GB. That is it's current size.
I have been using Lightroom since release 3.
It appears that unlike previous upgrades to Lightroom, my existing preview cache was not carried forward with the new catalog.
The new catalog no longer has a number associated with it, and neither does the previews folder.
So it appears that my previous Lightroom 5 Catalog Previews folder was abandoned with the upgrade to Lightroom CC.
If that is the case, then it is consuming 25GB of disk space for no purpose, and I can delete it to free up some space, correct?
I chatted with Adobe Support later this morning, and asked why Adobe did not carry forward the previews cache with this most recent upgrade.
Their answer - "the earlier versions for lightroom were not creative cloud based".
Though that is true, it doesn't seem like a good reason for this behavior, unless there was some sort of compatibility issues between releases.
In any case, he confirmed that the old cache was not being used and could be deleted.