Don't send membership expiring or expired emails for certain levels.

disable_membership_ending_emails_for_some_levels.php

/*
	Don't send membership expiring or expired emails for certain levels.
	
	Place this code in your active theme's functions.php or a custom plugin.
*/
function disable_membership_expiring_emails_for_some_levels($recipient, $email)
{
	//check template
	if($email->template == "membership_expiring" || $email->template == "membership_expired")
	{
		//check level
		if(!empty($email->data['membership_id']) && $email->data['membership_id'] == 15)
		{
			//membership expiring and level is 15
			$recipient = NULL;
		}
		else
		{
			//membership expired. get the user id first
			$user = get_user_by("login", $email->data['user_login']);

			//check the user's last level
			if(!empty($user->ID))
			{
				global $wpdb;
				$last_level = $wpdb->get_var("SELECT membership_id FROM $wpdb->pmpro_memberships_users WHERE user_id = '" . $user->ID . "' AND status != 'active' ORDER BY id DESC LIMIT 1");

				if(!empty($last_level) && $last_level == 15)
				{
					//membership expired, level was 15
					$recipient = NULL;
				}
			}
		}
	}
	  
	return $recipient;
}
add_filter("pmpro_email_recipient", "disable_membership_expiring_emails_for_some_levels", 10, 2);