We had that issue and for us some of it was caused by software issues and the other from hardware/ infrastructure issues.
1. This KB article may help - KB2775511 - https://support.microsoft.com/en-us/help/2775511/an-enterprise-hotfix-rollup-is-available-for-windows-7-sp1-and-windows There are about 3 hotfixes in there. To be honest, if we installed them manually it didn't seem to make a difference. Once the hotfixes were added to the image and we were able to reimage the computers we really saw a difference except for...
2. Computers that had the Broadcom 802.11n Wireless Network Adapter. Even with the hotfixes, these computers would take up to 45 minutes to log on! We had 2 models of computers with this card and both had the issue. The computers were purchased new around 2010. I was able to replace most of them with hand-me-downs that had Intel wifi cards and they log in with no issues. We have Meraki access points.