Add one of these code into the wp-config.php file.

Limit WordPress Post Revisions

define('AUTOSAVE_INTERVAL', 300); //seconds
define('WP_POST_REVISIONS', 3); 

Disable WordPress Post Revisions

define('AUTOSAVE_INTERVAL', 300); //seconds
define('WP_POST_REVISIONS', false); //false is Disable REVISIONS or by adding number limit in amount