How your team development IOS for my iphone?
Last 2 years my iphone 6 plus speed very fast . And then i always update my IOS BECAUSE I thrust in Apple softwares development team and now my iphone speed very slowly when i work in same application.
Over the years, excess clutter builds up, largely in the iPhone applications. Try restoring the iPhone.
Restore your iPhone, iPad, or iPod touch from a backup - Apple Support