If you are using a Realtor to sell your house, that is the person you should ask questions such as these.
If your sale closes on time, you should be o.k. not making the current payment since the entire loan will be paid off before the 15th of the month. If there are any delays, you might end up getting stuck with a late payment. Good luck and I hope there is no delay.
At the close of your sale, the amount that you owe to the HOA will be deducted from your sale proceeds, including any late amount and penalty if any is owed.