After removing all the tile, we had to spend 2 whole days removing thinset. It was fairly easy to remove from the part of the floor that is covered with a vinyl sheet. Not so much (and that's an understatement) from the concrete.
In the picture above you can see the part that we already scraped off (in the back) and the 16 ex-tiles we still have to scrape. It also shows some of the tools and protective gear we're using. You can imagine how sore we get after each day of doing this... I'm looking forward to start tiling soon!