Slow Microsoft Excel (Office 2016)

OK. Here’s what I mean by “slow Excel”. You will notice the lag after I press TAB from the 1st column, before the cursor move to the right.

Sometimes it’s so slow that it doesn’t register the key inputs and I have to repeat the keystrokes. (e.g. 1st line)

Disclosure: The worksheet performs lookup from another file with 900 lines of product codes (15 column attributes).