Decreasing output of a voltage doubler
Per the formula... +Vout will be

Vin = 9V
VL = 1.1V @ 100ma (Regulator loss)
Vdiode = 1V

+Vout will be 18 - (1.1 + 2) = 14.9
-Vout will be -18 + (1.1 + 2) = -14.9

For smaller (&lt;100ma) loads the VL will be less and the output voltage(s) will be higher.  

Keep in mind that this is a voltage doubler, not a regulator. The output will vary according to load and input voltage.