The cone will now hav a circumference of    pi * 30  -   pi*30 (144/360) = 56.549 units
     this will be a diameter of     56.549/pi   = 18        radius of  9  units
  
 the side length will still be 15  units
  
 sin of 1/2 of the vertex =  opp / hyp = 9/15   
    arcsin (9/15 ) = 36.87 degrees                              2 x 36.87 = 73.74 degrees