Acer ES1-111m-P2YU with 4GB RAM, conventional SATA 5400rpm drive, windows 8.1 upgraded to Windows 10, x64 [both].
Windows 8.1 would boot in ~20 seconds. Windows 10 boots up in not less than 60 seconds, and as long as 122 seconds [in the log so far]. I have set advanced Properties settings to favor Performance over everything, for system and for programs [though I'm not at the point of running many programs yet]. Power plan settings don't seem to make a diff. High Performance plan takes just as long as Balanced

Every unnecessary service is disabled, and Startup items: only one I left 'enabled' is the Intel DPTF
I note that Acer also has its own Energy saving service "epower" which kicks off a few processes.

in the Events log, under Applications & Services, Microsoft, Windows, Diagnostics - Performance - full of warnings and criticals and Errors - most of which are merely reporting out-of-bounds Boot Performance and Shutdown Performance. Along with these are a few errors re: Services that take too long, decaying boot up. these seem to change with every boot - so there is no pattern. though some are repeat offenders, they are not repeat offenders on successive boots : one here, one there.

i've tried some of the standard "fixes" like disabling fast boot and enabling fast boot - no diff.

how to debug?

also, in the system event logs there are no significant errors, and no device errors.