Memory Limit error upon activation?

Hi, just purchased ‘Developer’ license, upon activation am getting mssg:

Sorry, Microthemer requires a memory limit of 16MB or higher to run. Your memory limit is less than this. Deactivate Microthemer to remove this message.

I am keeping my config data in custom file above public_html and including file into wp-config in public_html

Our current wp-config looks like this:

<?php
define('WP_CACHE', true); // Added by WP Rocket
/**
 * The base configurations of the WordPress.
 *
 * @package WordPress
 */

/* That's all, stop editing! Happy blogging. */

/** Absolute path to the WordPress directory. */
if ( !defined('ABSPATH') )
	define('ABSPATH', dirname(__FILE__) . '/');
	require_once(ABSPATH . '../XXXXXXX/XXXXXX.php');

/** Sets up WordPress vars and included files. */
require_once(ABSPATH . 'wp-settings.php');

In my custom config file, I have set

define( 'WP_MEMORY_LIMIT', '512M' );
define( 'WP_MAX_MEMORY_LIMIT', '512M' );

There is no memory issue, and adding the above defines directly to wp-config resolves the error message…

We’d rather not have to bring these defines back to the standard location (we try to keep as much as possible out of wp-config) – please advise if some workaround is possible =)

Kind Regards, Max