Power Query load times get longer after edited steps

Well, "AND" statements take longer in every system, and in your case, you have two "if" equality tests as well. So in your original query, one column gets searched once. In your second query, you search the first column, and if false, then first column again, along with another column if that "if" predicate is true. Instead of looking for a value in one column, the query now has to look through one, but maybe two, or maybe three.

--Nate

I have found that the query load only begins to take a very long time when you start merging / appending tables that contain structured columns (the ones that you can expand to access data in linked tables). 

When removing these before performing the merge the load times are drastically reduced.