I assume you have set the dashboard url as the Fully Kiosk browser’s screensaver web url, so that dashboard web page is displayed as screensaver and will refresh at the rate you specified rate. You can always create a separate dashboard with another media and higher refresh rate to be displayed as screensaver if that’s what you want to achieve. 
Just in case you haven’t seen other community posts yet, TinyCam and Blue Iris are commonly used to feed the MJPEG source to the media tile for the better “streaming” experience, so you might be interested to these posts as well.
And our KB article about our media tile.