WWDC 2015 Event's Live Stream
Apple TV has an Apple Events channel with what appears to be all of the live streamed events and no requirement to have a developer account. The keynotes are traditionally available freely during and after the event. Whether the other content remains online post event is yet to be seen.

Otherwise, you can view online at https://developer.apple.com/

These seem to be tied to a developer program AppleID.

WWDC Session Videos

Watch the film "The App Effect"

View the schedule