defender can't run

Keep getting this message "Your server resource usage is too close to your limit. Please try again in 15 minutes." So what specifics resources need to be increased in order for this to function?

Also, we're not getting any alerts when the site is hacked. Getting injections of porn links into the homepage periodically. What makes it really weird is that when I clear the cache with W3TC the injected text disappears. Which makes me wonder if that plugin itself is compromised.