My masters thesis is 25k (excluding bibliography but including references and appendices). No "give or take", it's a maximum. We can go under if we want (though it has been suggested to not do it by much) but not over. Quite honestly, it sounds a lot compared to the above but I am glad for it as it really allows me to get into the meat of it. If I had to limit it to 15k it would feel very superficial, though I guess I would have not chosen quite the same topic in that case.