A star moving in the opposite direction of us that emitted light 15 billion years ago that we are just now seeing has moved a lot further away in that 15 billion years it took that initial light to reach us.
The correct calculation involves an integral, an example of which you can see here:
http://www.wolframalpha.com/widget/widgetPopup.jsp?p=v&id=45...
Not necessarily. By the time the light arrives here, its point of departure (and parts of its path through space) may have receded because of cosmological expansion, so its total travel distance, and its velocity, are no longer synchronized as they would be in Newtonian physics.
Your remark would have been true for the static universe that Einstein believed to exist when he proposed the first version of the cosmological constant (before 1929).