There are plenty of Causes behind the quickbooks running slow problem, some of them are listed below.
QB is not updated.Your computer does not meet the system requirements.Your company files have reached the maximum size limit.The QBWUSER.INI file is damaged or missing.Firewall settings are misconfigured so they restrict various processes to function properly.Some program files or QB Desktop installation is damaged.Your hard drive is corrupted.The Windows operating system is damaged.Let’s troubleshoot each one of these issues starting with the first one.To rectify this problem you need to find the best solutions like mentioned on this page about QuickBooks Running Slow.https://accountingerrors.com/quickbooks-running-slow-fix/