To avoid paying interest on your credit card purchases, you'll need to pay off the balance, as it stands on the 14th of the month, in full by the 28th of the month. That effectively gives you up to 45 days interest-free for purchases made from the 15th of the previous month to the 28th of the current month.
Cash advances are different as there is no interest-free period on them. So, if you withdraw funds from an ATM or transfer funds out of your Visa account, then interest will accrue from the date of the transaction.