Many people state that kivy is slow. While this may be true it is mostly due to that python is slow to run on android devices.Thus it is in the programmer's hands to properly optimize their code so as to create a performant application.
Most of the lag on android devices runing kivy apps arise due to widget creation. Widget creation remains the slowest step in a kivy app. Here are some of the methods that I follow to optimize my apps and ensure I can hit 60fps even on old devices