automation send email after a number of days

I have an automation that is supposed to send out an email after 15 days from the initial date (Open Date). Its purpose is it let users know the item has aged 15 days. For some reason the automation will also go out when I delete the date from the field. It is set at "Any Value" for the date field. Could this be causing the issue? The only other options are Blank or specific dates. Any ideas how to have the email go out at 15 days?