At saturation 1.5 x 10^-4 moles caF2 have dissolved in 1L of water. What is Ksp for CaF2 at this temperature?
CaF2(s) ==> Ca^2+ + 2F^-
Ksp = (Ca^2+)(F^-)^2
(Ca^2+) = 1.5 x 10^-4 mols/L
(F^-) = 3.0 x 10^-4 mols/L.
Plug into Ksp and solve. Post your work if you run into trouble.