You can use different qvw document to load data, and another as a vizualiser. Create 1 loading qvw per table and store your data into .qvd. Then load your .qvd in the final document.
if you want to reload your 4 documents at the same time, create a batch for each one.
With this solution, you will divide your reaload time by 4 and using .qvd then is easy to design your app.