Hi there, @neelteja.
It seems that your Mattermost instance is unable to reach out to the database server that you have configured in your config.json. May I know if the database server is hosted within the same machine or on a different one? Do you happen to have any firewall blocking the Mattermost server from communicating with the database instance?
The easiest way to know if the servers can communicate with each other is to run the following command from your Mattermost instance backend:
echo | telnet 192.168.1.15 3306
By default, you should be able to get the following result as an example:
vagrant@mattermost:~$ echo | telnet 192.168.1.15 3306
Trying 192.168.1.15...
Connected to 192.168.1.15.
Escape character is '^]'.
Connection closed by foreign host.
Can you please share the outcome of the test? Thanks.