Hi @aujjwal-smarsh,
Without any more details it’s hard to offer specific advice. One option you have is to test higher settings of the -parallelism flag. The default is 10, but if your configuration contains a lot of resources that can be concurrently updated and the remote API allows it, increasing that can speed things up considerably.
A lot has changed since v0.12 too, so if you are running into internal limitations within terraform, upgrading to a current release may provide some extra benefit too.