I've often wondered this myself. However, two potential problems come to mind in extending 15L/33R. First, I know there is a steep grade between the start of 33R and the start of Rwy 28. It doesn't show up very clear on a map, but I know when I've been looking out my window taxing for takeoff on 28 it seems like 15L/33R is going downhill in comparison to us. (Although, try zooming in on the point in question on a google map and maybe you'll see...) Not sure if this grade difference would impact an extension.
Second, and this may be a fairly minor point, but I'm sure the general aviation people over at Signature wouldn't be too pleased about extension and increased use of the runway they pretty much get to themselves now. Aside from US and AC
commuter operations I can't remember seeing another commercial plane use the runway.
I seem to remember talks of a parallel runway to 10/28 anyway, but it's been a long time since hearing that.
You don't need a passport to know what state you're in...