Are there individual memory allocations for different user roles in WordPress?

Because of this line in wp-admin/admin.php:

if ( current_user_can( 'manage_options' ) ) {
    wp_raise_memory_limit( 'admin' );
}

In other words, WordPress raises the memory limit to WP_MAX_MEMORY_LIMIT within the admin, but only for users with the manage_options capability i.e. administrators.

Your best bet is to raise the default memory limit in your wp-config.php:

define( 'WP_MEMORY_LIMIT', '256M' );