wp_nav_menu eats a lot of memory

I'm investigation some memory leaks into a custom wordpress theme . I noticed that the first menu displayed (for mobile) - eats around 7mb.

this is the mobile menu code (hidden for resolutions under x px)

 print number_format(memory_get_usage()).'</br>';
            wp_nav_menu( array( 
                'theme_location'  => 'mobile',               
                'container'       =>  false,
                'menu_class'      => 'mobilex-menu',
            ) );
 print number_format(memory_get_usage()).'</br>';

displays

37,299,320

44,254,368 - around 7mb used!!!

After the mobile menu i show a normal web menu in primary location.This is the "default" menu code

 print number_format(memory_get_usage()).'</br>';
       wp_nav_menu( array( 
                      'theme_location' => 'primary' ) 
                   );
 print number_format(memory_get_usage()).'</br>';?>

shows 44,317,656

44,553,176 -

If i remove the mobile menu code the default menu script prints 37,367,472 44,300,472 - around 7mb

Is it normal for wordpress wp_nav_menu() to take around 7mb of memory for showing a menu ? Can i lower the memory usage for it ? For the above tests i used the same 2 level menu for both locations. Thanks