RPGVXAce RTP is a group of files you can install independently of any individual game. Basically, it was a way to reduce download sizes, as you don't have to redownload a bunch of files with each update (or even for any game made with VX Ace which uses the feature).
The download you need is linked at the end of the game's page (under "install instructions"), but here is the link, in case you still have trouble finding it.
https://s3.amazonaws.com/degica-downloads/RPGVXAce_RTP.zip