If there would be a static optimal configuration, wouldn't it be standard already? What the optimal settings are for you depends on your system.
If your goal is to reduce user-perceived 'lag', any improvement as a result of changes to the default pocketmine.yml settings will be insignificant compared to getting a faster CPU, a faster hard drive, and a faster network. Other things you can do are convert mcr/mca worlds to pmanvil format, border the spawn world, optimize your opcache settings and on Linux set 'swappiness' to 0, and I'm sure I've missed things