Source: http://fragdown.esportsify.com/forums/informations/82259/fix-quickbooks-update-error-15215-server-not-responding
Trying to update QuickBooks to the latest release, but failed miserably and also encountered QuickBooks error 15215. Well, this is one of the most common situations that the user face, as per the recent observations. The user often faces this issue, when performing the payroll update or maintenance release. When the window displays this issue, an error message appears on the screen stating that the server is not responding to it or limited access.
Error 15215: Unable to verify digital signature.
You may also see this error message on your desktop screen:

In case you are seeking for a perfect solution to this QuickBooks error 15215, then you have landed on the right place. You can also update your QuickBooks desktop to latest release to fix this error. Moreover, you can also reach out to our QuickBooks professionals via our toll-free number i.e. 1-888-383-0323 and let them handle the issue on your behalf.
Follow the below given steps in order to resolve the error code 15215:
The user can resolve the error by verifying TLS 1.0 settings. The steps involved in this are as follows:


Running QuickBooks Desktop as the windows administrator tells Windows to allow QuickBooks Desktop to use any resources necessary in order to work properly.
Other than the above stated methods, there can be a couple of methods that can help the user in successfully resolving the QuickBooks error 15215. For that, you can contact us at our toll-free number i.e. 1-888-383-0323 and ask our experts to provide you with the most relevant solutions.
Our QuickBooks payroll customer support team will be there to assist you in a single call.
You"ll also like other article:
How to use QuickBooks connection diagnostic tool?
Methods to troubleshoot QuickBooks error code 6000 82