Very Slow Boot

I do have Dell Inspiron 3542 laptop.
I have dual booted my laptop with Windows 10 and Ubuntu 15.

My Windows 10 boots very very slow.

First it shows me windows sign and loading screen then it goes "blank" for like 1 minute and then comes the login screen.
After entering password it takes like 1 minute to come to desktop.
When desktop comes then it takes like 1-2 minutes to load all desktop icons and taskbar icons and it takes 2-3 minutes more to become stable.

I've tried everything to optimize as suggested in various websites and guides.

- I've fast boot enabled.
- I've disabled each and every service at start-up(even my antivirus) - from task manager.
- I do optimize my laptop regularly removing temp files and fixing various issues.
- I've also disabled various background services (from "msconfig" tool).

Still it boots damn slow. Before becoming stable if I click on any icon or right-click it hangs sometime and it becomes big headache.

I had Windows 8.1 before which was working fine. ( It was also dual booted with Ubuntu).Then I upgraded to Windows 10 using free upgrade.

Also it show 100% disk usage ( in task manager) for first few minutes when desktop appears. (After that it comes down).
I checked my hard-disk for errors (via Dell system checkup), its fine.

I don't know what to do. I want it to boot fast. Please provide me solution or provide some steps to follow in order to increase boot performance.

Do you have hibernation on? For fast boot to work hibernation must be on.

I turned on hibernation and it booted fast.
Thanks.
But the thing is I have to turn off fast boot in order to access windows drives in Ubuntu.
So after turning off fast boot, it boots very damn slow.
Is there anything I can do in order to boot fast without enabling fast boot? Because it boots very very slow. takes like more than 5 minutes to become stable which is horrible. .
One of my friends suggested me to continue without doing any changes, after few days of usage the boot time will improve automatically( because he was facing the same problem but after few days of usage his boot performance got better)....is this true??

Don't really know if that's true or not. On a fast boot Windows uses the hibernation file for it to work. No harm in trying your friends suggestion. I don't use any other OS' so I'm not familiar with the impact Ubuntu has on WIn 10. Five minutes seems extremely long even for a slow-boot. If I slow-boot, or restart, it usually only takes about 1:15 or so.