  We present the results of electrical transport measurements of
La$_{1.85}$Sr$_{0.15}$Cu$_{1-y}$Ni$_{y}$O$_{4}$ thin single-crystal films at
magnetic fields up to 9 T. Adding Ni impurity with strong Coulomb scattering
potential to slightly underdoped cuprate makes the signs of resistivity
saturation at $\rho_{sat}$ visible in the measurement temperature window up to
350 K. Employing the parallel-resistor formalism reveals that $\rho_{sat}$ is
consistent with classical Ioffe-Regel-Mott limit and changes with carrier
concentration $n$ as $\rho_{sat}\propto 1/\sqrt{n}$. Thermopower measurements
show that Ni tends to localize mobile carriers, decreasing their effective
concentration as $n\!\cong0.15\!-\!y$. The classical unmodified Kohler's rule
is fulfilled for magnetoresistance in the nonsuperconducting part of the phase
diagram when applied to the ideal branch in the parallel-resistor model.
