After i tried to find whats problem in wp-admin, i found w3 total cache's wp-content/object-cache.php file is "the reason" for admin page slowing.
How i test it:
Disabled w3-total-cache; admin pages speed is good.
Enabled w3-total-cache; admin pages are slowing so much.
Enabled w3-total-cache and deleted wp-content/object-cache.php file; admin pages speed is again good.