Can be unreliable irregardless of the operating system. I'd try HIBERNATE next.
But 15 to 30 minute boot times is telling.
For example my 2006 Dell Inspiron e1505 with 2GB RAM, CoreDuo CPU, and 120GB SSD boots from cold in 33 seconds to when I get a google search result. That's all that way from power off to a web page result in 33 seconds.
I would have to guess your PC is much older and far worse than my oldest laptop?
Ever since upgrading to Windows 10 from Win 7 Pro I have been having issues with rebooting. When I leave the office I dont power down, I just put my machine to sleep so that when I get home I can carry on working. With win 7 there was no issue with this, now with windows 10, when I try "Wake up" my laptop goes into a boot cycle as if I requested it to restart. The reboot takes about 15 -30 min every time. I have tried to find a solution for the issue but cant find anything.
I recently discovered that windows 10 has issues with AMD Radeon graphic cards but my drivers are up to date so im note sure what the issue can be. I have had issues with my graphic card in the past.
Im on the brink on formatting and going back to windows 7.
If anyone can give me some guidance on how to fix this issue I'll appreciate it.