It is time consuming to delete huge number of files by rm.
rsync is more efficient in doing it.
You need to create an empty directory first:
mkdir /tmp/empty
and then run rsync:
rsync --delete-before -a -H -v --progress --stats /tmp/empty /path/to/your/dir
You are expected to get tremendous performance improvement.
But rsync is not more efficient thent rm in deleting a file huge in size.
The recommended tool is echo.
You can delete the content of a file by echo nothing to it:
echo > /path/to/your/file