If it was a bloatware HP you upgraded from the HP image then it would have a heap of HP tools installed, many of which will be hooking into explorer. By hooking I mean they have registered programs that intercept messages to explorer or start bar or the system tray. They do this to "try" and be smart in how they interact with the system so they can perform actions based on what you do. If one of those tools isn't completely compatible with win 10 or has a bug you will see delays or errors or freezes in explorer, start meny etc.
personally well I get any sort of OEM supplied machine for myself or for someone else the first thing I do is nuke the installed OS from orbit and do a clean install. barring that try removing some of the unneeded HP tools from the control panel add remove programs. you could also try going to HP website and making sure they are all updated.
I do have some bloatware left (I deleted most of it when I had Windows 7) but I think what solved the problem was turning off Cortana and unlink my computer from the Windows account back to a local account. Now the OS works pretty well and the Start menu doesn't lag like before. And the search bar opens everytime I click on it. Also, I'm opening some programs and a game I had before and they work well. So far, so good. I hope the updates fix Cortana, because I was looking forward to use that function. Thank you.