Find the best fit with some conditions

I'm not sure why FindFit can't manage it, but if I construct the objective function myself to minimize square residuals and I use Method -> "DifferentialEvolution" then I get the answer:

objective = Total[(#[[2]] - b[#[[1]]])^2 & /@ data];
fit = Last[NMinimize[{objective, conds}, {l, j, s}, 
  Method -> "DifferentialEvolution"]]//Chop

(* result: {l -> 0, j -> 1.5, s -> 1.5} *)

However, using FindFit's Method->NMinimize I was unable to achieve the above result.