Dell XPS 8700 very slow wakeup

I am running Windows 8.1. Every time my XPS wakes up from sleep, it takes almost 2 minutes. It's so annoying. My old system XPS 8300 takes only about 30 seconds. I have installed the latest drivers and bios I can find on the Dell site.

I have also complained this to Dell Tech Support. But the guy would only suggest me to format my HD and reinstall the OS, which I did. But it doesn't help at all.

Has anyone had this issue? Thank you.