The Recovery drive is part of the installation from HP - it is where the "original" files are located. If you use the HP recovery, this drive is where it goes. If you ever want to use that feature, do not delete that drive or any files in it. The reason it is almost "full" is that is the space needed for the recover files, nothing else.
If you don't every want to restore the HP installation, then remove the partition and add the space to your C:\ drive. Just know that the recovery option will no longer work.