It depends on the source of the funds and also the amount. And these days it is because banks and others are risk averse; they won’t process too quickly to make sure there is noting untoward in the transactions.
Three days is kinda normal.
If your cc is due on the 14th, and you pay it on the 14th, the cc company will note that you paid on time, but it may take until the 15th before the bank processes the transfer, and then the cc company will not post until the 16th. That’s because they process transactions in batches, not individually.