So, as per your suggestion I'll update my database from 9.1.2 to 9.1.15.
Kindly confirm, which year this 9.1.2 was released and when 9.1.15 was released.
And easily I can upgrade this and what are the steps to upgrade, kindly confirm?
On disk format for the same major version is compatible, so simply install the new binaries and restart your server. The installation of the new binaries depends on your OS and/or the way things have been installed.