QuickBooks payroll error 15215 typically occurs when there is a conflict with another application running in the background, often related to Internet Explorer settings. This error can also arise due to issues with digital signatures, incorrect configuration of firewall or antivirus software, or problems with the Windows registry. To resolve it, ensure that QuickBooks is running as an administrator, verify Internet Explorer settings, configure firewall and antivirus software correctly, and update digital signatures and Windows registry settings. For persistent issues, consult QuickBooks support or a certified professional for assistance at 1.855.409.2300.