How do I Maximize File Efficiency

I work with data sets that I typically look at forecast by year. Currently when I look at 2026 and 2027 it is rougly 1.4M lines of data. I have to put these in two separate data pulls and tables. Then I have six different customers included in this data. so I have to create 6 tabs with six diffrent pivot tables for them to look at. This has created a massive file that lags just to open, save or close so I really have two questions and am open to suggestions.

1. Would it be better to store the data in one worksheet and then link a second worksheet that just has the pivot tables and separated look? If so how would I creat that link?

2. Can you explain to me like I am 5 how I would use power query to combine the 26 and 27 table so that they could be in the same pivot table? Every column in both are identical.