i just went through this exact same problem with
Word 10.1.5 running suddenly very slooooowly.

Interestingly running Word from a different user account (guest, for example), was perfectly fine. This is the main clue to the problem.

Turns out that Word is highly sensitive to problems in the Entourage mail database. This seeems to cause the slowdown (WHY Word is dependent on the Entourage databse is beyond me - ask MS why they have created this dependence!!!).

To confirm it is the Entourage database causing the problem, first quit Entourage. Then remove the offending account folder from ~/Documents/Microsoft Office User Data/Office X Identities temporarily (drag it to the desktop), then relaunch Entourage. Entourage will automatically recreate a "Main identity" folder in the "Office X Identities" folder, and you will find Word will suddenly become much more responsive again. A rebuild seems to fix this problem.

Another thing to consider... MSOfficeX runs a search throughout your network for duplicate copies of itself running on another computer. This prevents two computers from running the same copy of OfficeX at the same time.

Is there any reason for MXOfficeX to have a problem conducting the network search which is causing it to hang and slow things down?

That's weird. But I offloaded my entire Entourage folder to another hard disk, emptied the trash, and Word runs as fast as I could hope for!

That's just WEIRD.

But thanks!!!

One more problem that slows Word v.X down hugely at launch - Adobe Acrobat 5.0 installs a file called pdamaker.dot into the Word folder inside the MS Office/Office/Startup folder. Removing this file also greatly speeds up the startup of Word. As far as I can tell, it is totally redundant under OS X anyway - probably was developed for Office 2001.