Ubuntu very slow boot after chaning driver (Nvdia)

I previously used X.Org driver for my Ubuntu desktop, and my graphic card is Nvdia GTX 1070, actually I’ve never been satisfied with my boot time because I use an high-end SSD and the boot time always takes more than 20 s (comparing to my Ubuntu laptop which is Radeon graphics and the same SSD, only takes 9 s).

However, recently I met some problem with compatibility issue of RStudio (always crashed) and I had to change to Nvdia driver as it was described here. So the Rstudio no longer crashes, however I face a very slow boot, after entering the grub (I have dual-boot), it freezes about 30s, and then the PC has a very transient beep (shorter than the boot one), and then I had to wait another 30 s until I can enter the login.

Does any one know how to solve this issue?