Chevereto current requests takes an average 0.9MB RAM and 0.07 seconds which is already pretty fast and lightweight. You usually need caching when the load is bigger like in Wordpress (more tan 20 MB RAM) or in Drupal (near 40 MB RAM). For Chevereto isn't an issue at all because like I said, is already fast and light without anything on top.
Also, making your website slightly faster has nothing to do with pagerank which depends on how many in/out links your website has.