I think the extreme CPU usage is related with these errors:
29/08/15 08:35:42,153 Microsoft Word[2349]: Cocoa scripting error for '0x024a0182': four character codes must be four characters long.
29/08/15 08:35:42,153 Microsoft Word[2349]: Cocoa scripting error for '0x024a00e0': four character codes must be four characters long.
29/08/15 08:35:42,153 Microsoft Word[2349]: Cocoa scripting error for '0x024a0126': four character codes must be four characters long.
29/08/15 08:35:42,153 Microsoft Word[2349]: Cocoa scripting error for '0x024a012a': four character codes must be four characters long.
29/08/15 08:35:42,153 Microsoft Word[2349]: Cocoa scripting error for '0x024a0175': four character codes must be four characters long.
29/08/15 08:35:42,154 Microsoft Word[2349]: Cocoa scripting error for '0x024a012c': four character codes must be four characters long.
29/08/15 08:35:42,154 Microsoft Word[2349]: Cocoa scripting error for '0x024a0067': four character codes must be four characters long.
29/08/15 08:35:42,154 Microsoft Word[2349]: Cocoa scripting error for '0x024a00dd': four character codes must be four characters long.
In my logs hundreds of such messages were found generated with the same time stamp.
MS-Word 15.13.1 and OS X 10.10.5.