If you hadn't said you get the same delay with QuickFill off, I would have said the Memorized Payee list sounds like it could be, at least, part of the problem.
But, my understanding has been that there is a limit on the Memorized Payee list that probably wouldn't allow anywhere near that number of payees.
You can test your theory easily. Backup. Delete all your Memorized Payees. [You can select them all as you would select multiple files in Windows Explorer.] See what your response time is like with no Memorized Payees. Revert to your backup.
If the empty Memorized Payee list brought much faster response time, plan to cull your existing list.
[Also consider the possibility that there may be some corruption in the Memorized Payee list ... you might be able to get an idea if this is true by Validating a Quicken Copy of your data, and testing in the Validated Copy. On the off-chance that the Validate improves response time, make the Validated Copy your regular file.]
BeanSmart website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.