I'm happy to have 1,5 Terabyte of wow files on my PC

Keep it up blizzard.
I want more downloads everytime I turn on the wow launcher, give me at least 10 Terabyte worth of wow files. GOGO

I’m assuming you are pointing at the client constantly downloading background-data without ever stopping? I had that problem, too, for a while. Deleting the entire WoW installation and re-installing solved it for me.

Now it’s 74 GB for me.

This.

It works. You can do it from the battle.net interface, click the settings button underneath the title on the game page and do a uninstall/reinstall.

Nope, every time I close the game down it automatically finds a new location to install wow, and downloadsd another 68 GB.

That sounds pretty annoying. Do your drive letters frequently change?
What is the pattern of those locations?
And what’s the default location set in your battle.net client?

You can enforce a location in your battlenet settings: