Did have different between about ios device or any version influrrent performance problem?

Hello guys, I have a problem when using ionic vue version 5 to build a project. Then after all I have almost done and make a final test on my iPhone 6 Plus, iOS 12.5.

When I’m testing app on iPhone 6 Plus, iOS 12.5. I realized a big problem about performance, router to another pages very slow (sometimes delay 3-5s) and sometime rendered pages have sort by sort like rendered header and body first, and then rendered footer, obviously.

But when I transfer to iPhone 7 plus with iOS 15.2. Everything is turning back to normal, performance not so much evident anymore, and the router without delay like I was using iPhone 6.

Can someone’s helps me out by this problem.