I do not believe the first copies of AC 15 will be shipped until early/mid June according to Graphisoft's press release. http://www.graphisoft.com/community/press_zone/ac15.html Last year the software was announced in May and we did not receive it in the US until July. The trial was not downloadable from myarchicad.com until then either.
Alpha testers have been using it since the first 'work in progress' version was released last July. Looked a lot different then though and no production work came out of it. Trust me - it really was a work in progress!
Makes you realise just how far ahead Graphisoft is planning these releases. A lot of (paid and unpaid) work goes into them!