Slow refresh with small excel as source

To be honest,  on first sight I don't see any code that would directly explain the slow refresh.

10mb doesn't sound as a small Excel to me though. What are the numbers of records?

I assume that the final result is what you require?

So in fact "Hechos" is not 55x the number of records from "Maestro", but about 3x.

This is what I would try:

1. Use Table,Buffer for Source and each of your 4 tables.

Source = Table.Buffer(Table.SelectColumns(Maestro,{"Clau", "Estat", "Data Creat", "Data Actualitzat", "Data Entrega"})),

CreadasFinal = Table.Buffer(#"Creadas - Added Custom1"),

Likewise for the other tables.

OR:

2. Create separate queries for each of your 4 tables and an additional query to combine these.

Hope this helps.