Imagine there is a bomb in the room and you are trying to find an exit how to escape. We would try our best. Similarly we should chant our rounds in the same spirit that Maya is ready to attack, so we must try our best to surrender to Krishna.
Actually 16 rounds is nothing. Chaitanya Mahaprabhu said 64 rounds.
If by the tongue you chant Hare Krishna mantra and by the tongue you taste prasadam, you will be perfect, simply by executing these two things.
As soon as a devotee can chant the holy name and glories of the Supreme Lord, he certainly comes to the liberated position. Attachment for glorifying the Lord by hearing and chanting the holy name and activities of the Lord (Sravanam Kirtanam Visnoh) certainly brings one to the position where material contamination is absent.
Just like we need food for the body, we need food for the soul and what is that food? Hearing and chanting God’s names in the association of saintly people. Otherwise, we will give in to temptations at the smallest instance. We will be weaklings, spiritually.
There are two types of chanting: Offensive, where the result will be that chanting will be stopped in due course of time. While the other one is offense less chanting, where we will be inspired to always chant more.