It did not - an earlier German attack was not feasible, due to the unusually wet spring of 1941, and Germany had made the strategic decision to launch an attack into the Balkans that spring, due to political and military developments in the region. In addition, German preparations were not complete in time to allow for the 15 May invasion date.
Basically, Germany really couldn't attack any earlier than they did - the "delay" was unavoidable, given the realities of the situation. As it was, Germany failed to either consider or overcome the logistical nightmare that any invasion of the USSR was bound to become (due to the vast distances that needed to be crossed, the poor state of the Soviet road and rail networks, the spring and fall mud seasons, the massive armies required by both sides, and so on), and had no means with which to really improve these problems (due to German industrial weakness and lack of resources).
The USSR was simply too big, too populous, and too industrial for Germany to handle without a complete collapse of the Soviet government (and, unfortunately for the Germans, this didn't happen).