Just thought of another way to 'offload' cron **without load balancing** ...
clone the code directory to your dedicated DB server. Apache server will not be used in running cli cron nor any of the cli scripts contained in code. You would have to change the config.php file of the clone ... moodle checks and in this instance you could use superuser creds for DB. A moodledata directory would need to exist ... one could use a mount point on the DB server that points to the real moodledata on the web server.
One ***never uses apache*** ... apache service isn't running ... use only CLI scripts ... NO browser.
Since, in your case, top/htop or whatever has shown your DB server is basically under-utilized memory wise one has much more resources available to cron than the balancing act one has to do on web server.
'spirit of sharing', Ken