It may be an issue with your .pst file. Presumably, when you reinstalled Office, you told Outlook to hook up with your original .pst file? You may want to see what happens if you back up your existing .pst file somewhere (call it outlook.old or something) then get Outlook to create a new one. If Outlook then runs faster, you may well have identified the cause of your problem.
Amazon Fire HD 8 review: A brilliant combination of function and value – with one massive caveat