Office 2016 slow to launch

Thanks for everyone's help with this. I'm sticking with 2011 for now...

I may have found a fix to this problem.  I believe the Keychain entries for Office were corrupt, duplicative or otherwise problematic.

Fix:

I open one of the Office apps (Word in my case) and signed out completely from Office 365 and OneCloud (I have a personal account as well as an Office 365 OnceCloud account).

I closed Word (no Office apps are now open).  I opened Keychain Access, searched for any entries in Keychain with the word "microsoft" in it.  I had several entries related to Office and OneDrive/Office 365.  I deleted all of them.

I opened Word again, signed into Office 365/OneDrive.  I then opened each of the other Office 2016 apps (Excel, PowerPoint, OneNote; I do not use Outlook but open it, too, if you do) one at a time.  In each instance the icon will bounce in the Dock for a quite a bit then a dialog box will appear asking you to allow access to a keychain entry (multiple entries if you are signed into multiple accounts like me); reply "always allow" to each dialog box request and the app will finish opening.

After doing this for each Office app (and closing each app), I opened each app again and the time to launch was significantly shorter; in fact, what I would call "normal".

I rebooted my Mac and launched Office apps again.  This time no app requested keychain access and each launched quickly.  The second launching was very fast indeed.

I recognize this may not be the root cause for everyone's posted issue, but I hope this approach may help others.  In any case, it does not assume you use an AV application or anything at all. Period.  Every Mac uses Keychain, so this is likely a fix that can work for may people who have slow app launch issues.

Thank you Campy11.  Your solution worked for me.

I, recently, upgraded from Office 2011 to Office 2016 in preparation for upgrading my Mac to High Sierra.  No complaints (so far) about 2016.  When the apps are open, they're working smoothly.  But the act of, actually, opening them was taking forever.  Maybe 30-60 seconds after dozens of bounces in the dock.  Quitting the apps was, also, unusually slow.  A quit would close all of the app windows, but I noted that it would take, maybe, 15-20 seconds before the indicator next to the icon in the dock would go away.

I thought that I had, completely, uninstalled 2011.  However, when I went into Keychain Access, I noted that I, still, had a couple of keychains that would have been associated with the older version of Office.  I suppose those could have been borking things.  I deleted all the Microsoft keychains and relaunched the apps one-by-one.  I never got a dialog box asking for keychain access.  I, only, had to log back in to the first app that I relaunched.  I was, automatically, logged back in to the others upon relaunching.

Now, the apps are launching after a handful of bounces and quitting is instantaneous.  Close enough to "normal" to please me.

OK you finally convinced me to look at the security programs.  I turned off Norton Security - no change, still 30 second initialization times.  Quit Malwarebyes (Premium), up comes do you want Malwarebytes to change your system --> YES, start Word 2016 and my god I am back to 5 second program loads/initializations.  It must be Malwarebytes Premium!!  Restart machine to see if Malwarebytes was uninstalled when I checked the Quit Malwarebytes option (right click on Malwarebytes system tray icon).  No, as expected Malwarebytes is back in the fold after the restart (I didn't uninstall since I wasn't asked to uninstall Malwarebytes Premium, just quit Malwarebytes).  But guess what? The Office program initializations are back to 5 - 10 seconds which was the performance prior to the Version 1709 update of Windows 10 Pro.  Somehow stopping (Quit in Malwarebytes terminology) and restarting Malwarebytes (by doing a computer restart) seems to have fixed my 30 to 60 second Office program initialization issues.  Guess I will have to ask god why this fixed the Office Pro 2016 program load/initialization problems.  Checked this solution on my two other machines and it works on them also - the Office programs are back to their pre-1709 update initialization times.  I will ask Mr. Gates for forgiveness on this second Sunday in Lent.