Management timeout problem in Magento 1.9

Admin configuration settings:
System => Configuration => Web => Session Cookie Management => Set cookie lifetime 259200.
And

Go to => System => Configuration => Admin => Security => Set Session Lifetime = 259200 (seconds)

Clean up the Magento cache.

And made changes to the php.ini:
session.cookie_lifetime 259200
session.gc_maxlifetime 259200

After all these things, the administrator reported an inactivity of 15 minutes.