Your points are valid, and indeed 15 million deaths is the official estimate: scholarly opinions suggest the real number might have been 2 or even 3 times higher.
But perceptions of such matters become skewed by context. Given that the population of China was at the time somewhere around 6-700 million, this loss of life probably seemed marginal to the leadership of the time, and we might also remember that half a century ago the quality of information was considerably poorer; sputnik was the bleeding edge of satellite technology, and it's doubtful whether China even had computers, never mind a nationwide telephone network or even adequate roads.
Now this doesn't absolve them of responsibility, but nor do I think that such deadly economic calculus is limited to their adoption of communism. A century prior, when Britain was the leading global superpower, a famine wiped out the Irish potato crop for several years running (http://en.wikipedia.org/wiki/Great_Irish_Potato_Famine). The English government, which ruled there at the time, did nothing much about it, even though it could easily have been alleviated thanks to the proximity and availability of grain and other foodstuffs - indeed food exports from Ireland to England actually increased, because the native population were too poor to buy as crops had failed. The population collapsed, with about 1-1.5 million deaths (out of a population of only 8 million) and a similar number for emigration (which is why there are so many people of Irish descent in the US and Australia). Of course, in the context of the whole British Empire, this did not seem like such a significant number, and the government of the day viewed it as an embarrassment rather than a tragedy, to the extent of asking other countries not to bother sending food aid and attempting to blockade some that did so anyway.
Now at the time Britain was a limited democracy by today's standards and practiced mercantilism rather than a true market economy, and knowledge of agriculture and economics was basic; but the scope and severity of the problem was well understood, as recorded in parliamentary debates. It's a sad fact that having the basics of modern democracy and economic freedom do not inoculate any government from presiding over or contributing to monstrous levels of suffering in a misguided assessment of where its interests lie.
When we critique Marx and his intellectual heirs, as I agree we should, it's worth bearing in mind that he and his contemporaries had abundant reason to believe that capitalism was a morally bankrupt economic philosophy.