vec_set sets the vector of vector2 to vector1
vec_set(vector1,vector2);
so...
vec_set(camera.x,vector(-180,0,50)); //line 1
vec_rotate(camera.x,player.pan); //2
vec_add(camera.x,player.x); //3
camera.pan = player.pan; //4
camera.tilt = -15; //5
you're setting the camera.x on vec_set line 1st the 2nd line and the 3rd line,
use temp here then here instead of camera.x on those lines, then create a new line between 3 and 4
you may need to tinker with this slightly to get your desired effect!
Hope this helps