Yup. Even on S6 OC mode (overclocked mode), you will still get zombies. Maybe it's just the optimisation. The game has been better optimised of course but there's still room for improvement when it comes to zombies and huge packsizes. You can avoid the large mob groups by reducing packsize number to 130% or so and generally avoiding them.
What does definitely help is no shadows, Low fx or High (sometimes high fx makes it better in some cases but not often) . Also no screen shake since it's pretty intense on the CPU.
One thing for sure though, better hardware can reduce the chances of zombies but you still have to avoid the large mob groups. Also on devices with 46/62 loading first time, wait it out to reduce lag the next time you join the game. I had to learn the hard way with my old s3 mini before I had an S6.