To download a pdf of the current ISO 15919 standard (a 30 page document) costs 145 Swiss francs = 160 US dollars. I'm wondering if this is one of the reasons that most people use IAST for transliterated Sanskrit. The only place I've seen the ISO 15919 standard used in a book is Madhav Deshpande's sanskrit primer संस्कृतसुभोधिनी .