slow to start

Check into Glary's Utilities, clean all the bs and clear the browser caches, uninstall any software you do not use. Disable startup items not needing to start on boot.

Hi, first check the disk- Hard Disk Sentinel, trial - best text report I know of.

The laptop is supported for Vista and '7, apparently.

BIOS: make sure this is as up to date as possible.

Slow boots can be analysed using Windows Performance Recorder, free from MS.
Download and Install Windows Performance Toolkit in Windows 10 | Tutorials

There are examples of such threads (search for 'slow boot recorder' e.g.). The recorder gives a visual representation of the boot sequence in great detail.

Warning: this is a technically challenging task and not to be undertaken lightly. Even if a problem driver (e.g.) is found, the question may then become what to do about it.

Note: you may also wish to check the laptop can boot to and stay in Safe Mode, as this can reveal incompatibilities as well.

There is no guarantee of resolution as upgrading to '10 is using it out of spec.

Where does it spend the most time. Is it before Windows starts to boot or after? In other words, while the Dell logo is displayed or after it's been cleard and the Windows 10 logo has displayed?