Describe how to translate the graph of y=√x to obtain the graph of y=√x-15 shift right 15 units shift down 15 units shift left 15 units shift up 15 units

The parent funcion is:
 
 For this case we have two possible cases:

 Case 1:
 If the new function is:
 
 We have the following transformation:
 Horizontal translations:
 Suppose that h> 0
 To graph y = f (x-h), move the graph of h units to the right.
 
 shift right 15 units

 Case 2:
 If the function is:
 
 We have the following transformation:
 Vertical translations:
 Suppose that k> 0
 To graph y = f (x) -k, move the graph of k units down.
 
 shift down 15 units

I'm not sure exactly but my best guess would be 1/4