You want the day to be about the family, not the stress of the invoice. Start looking at venues and catering options at least three months out to get the best prices and lock in your date.
Big events like this can hit your bank account hard, so spreading the cost over a longer window can help you manage your monthly cash flow while you focus on the details of the day.
Remember that the 0% intro window is a deadline, not free money. If you do not pay off the full $1500 before the 18 months are up, you will start owing interest on the remaining balance at the standard rate.