It should be the bank information you provided on your most recent tax return, which in this case would be your 2019 return. The IRS Portal date confirmation is a little deceiving right now I would say. To my understanding, what that means is your stimulus was processed on that date. And when you look at the govt timetable site (that we have posted on another thread that addresses similar issues) it says they are depositing checks the following week for anyone that updates their info via the portal by Thursday.
I know that's not exactly your situation, but putting two and two together, it seems most likely the IRS will make deposits for everyone that got that message about the 15th actually the following week, from Monday April 20th to Friday April 24th.
Recommend continuing to check your accounts daily and hopefully by early next week you will have your stimulus.