Hello,
At what boot phase did you experience the slowness, before you enter your credentials or after ?
If before, may be caused by an outdated driver. Try to update your drivers (Wifi card, Video, ...etc)
If after you logged in, may be caused by a network issue; if you have a Microsoft account, create a local account and see if it solve your problem.
It can also be caused by slow program or service startup ...
you can also, run these command to repair you image system, if somthing is corrupted:
- sfc /scannow
- Dism /Online /Cleanup-Image /RestoreHealth
If none of this work, you can take a boot trace using Windows performance recorder
https://developer.microsoft.com/en-us/windows/hardware/windows-assessment-deployment-kit
Here is a tutorial on how to take a boot trace
https://zinetek.wordpress.com/2015/12/16/how-to-use-wpr-to-record-boot-sequence/
When done, share your boot trace and I'll help you analyze it.