anything over 10% is essentially a wall tile, it far to open and porous to go on a floor. Given its low breaking strength its really not durable enough
That's complete rubbish you cannot rest the tiles on the floorboards and tile. You need an expansion gap. Weight would be far too much for those walls needs overboarding as you said
100% agree it needs to be removed, also have you considered the square metre weight of the tiles on the substrate? If that's just normal plaster then it can only take 20kg/m2