wordpress extremely slow on NAS

I guess you already answered the question yourself. The other thing could be that your NAS has a slow harddrive (5.400 rpm) or that your connection is slow.

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Edit: Speed up with removing unwanted dashboard items…

<?php
/*
Plugin Name:    Dashboard-Widgets Removal Plugin
Plugin URI:     http://example.com
Description:    Disables admin UI dashboard widgets that you do not want
Author:         Franz Josef Kaiser
Author URI:     http://say-hello-code.com
Version:        0.1
License:        GPL v2 - http://www.gnu.org/licenses/old-licenses/gpl-2.0.html
*/
/**
 * Disable unwanted Dashboard Admin UI Widgets
 */
function oxo_dashboard_widgets() {
    if ( !is_admin() ) 
        return;

    global $wp_meta_boxes;
    // Right Now - Comments, Posts, Pages at a glance
    # unset( $wp_meta_boxes['dashboard']['normal']['core']['dashboard_right_now'] );
    // Recent Comments
    # unset( $wp_meta_boxes['dashboard']['normal']['core']['dashboard_recent_comments'] );
    // Incoming Links
    # unset( $wp_meta_boxes['dashboard']['normal']['core']['dashboard_incoming_links'] );
    // Plugins - Popular, New and Recently updated WordPress Plugins
    unset( $wp_meta_boxes['dashboard']['normal']['core']['dashboard_plugins'] );

    // WordPress Development Blog Feed
    unset( $wp_meta_boxes['dashboard']['side']['core']['dashboard_primary'] );
    // Other WordPress News Feed
    unset( $wp_meta_boxes['dashboard']['side']['core']['dashboard_secondary'] );
    // Quick Press Form
    # unset( $wp_meta_boxes['dashboard']['side']['core']['dashboard_quick_press'] );
    // Recent Drafts List
    unset( $wp_meta_boxes['dashboard']['side']['core']['dashboard_recent_drafts'] );
}
add_action( 'wp_dashboard_setup', 'oxo_dashboard_widgets' );
?>

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Edit #2:
Link to a debug plugin that offers time meassuring: Blackbox Bar