I believe the lag issues are fixed in the next version. I wouldn't recommend any less than 6gb of ram personally I have 8gb and 12gb on my devices and havent had any freezing issues
Viewing post in Hero's Harem Guild (NSFW +18) comments
If you want to do a quick and dirty solution, write a launcher to configure things like image cache sizes and various other settings. Some quick configuration tweaks and suggestions given detected hardware resources should provide an adequate performance boost. Reading O'Reilly's High Performance Python couldn't hurt, and there are some Ren'py performance guides too. When in doubt check out what the Eternum Dev is doing.