I’m actually very surprised that you are having performance problems like that. In particular, Flutter compiles to ARM code (not JVM) so normally startup is very fast. If you would file an issue on Github, we can figure out what is happening. https://github.com/flutter/flutter/issues
Update: I talked to some people here and they say that they have come across a few older phones that have performance problems like this. They will find a Sony Xperia ZL and see what’s up and fix it.
Thanks for the tip! Finding (and fixing) edge cases like this is why we have an alpha period. If anyone else has performance problems, please file a short bug report with the exact model number of your phone.