I usually test the game on a device with at least 6 Gb of RAM because it's pretty difficult to run lots of apps on your phone with the latest Android while having 4 Gb or less RAM. Speaking about improvements, the next update will feature a different type of compiler in Unity and version for ARM64 Android devices, so it should perform better, I guess. You can set the graphics quality to Low on your device and re-launch the app. Technically, Low graphics quality on Android means the usage of highly compressed textures in memory and it can help. Also, turn off post-processing and turn on the "ignore background bonus" flag in Settings, it will improve the performance of the game a lot.