I have the new XPS 12 with a intel 4th generation haswell processor. I saw that ultrabooks should resume from sleep almost instantly. My computer took longer to resume from sleep than fully boot up. However, if I disable intel rapid start technology (which should make the resume faster), the computer resumes almost instantly. I have the latest bios available for Dell.
Panani, please make sure your computer comply with all system requirements
My recommendation will be to contact your system manufacture, since this technology is normally configured by them when manufacturing the computer.