iphone 6 is slow performance

My iphone 6 is super slow after i update the 11.1.1, I don't know why the iphone 6 users are having this issues. Other model users are doing great with ios 11. Generally people are saying the A8 chipset users are having this slow performance issue. I don't know when apple will release the update for iphone 6 users. It's very difficult to use the phone. I have raised the case of still it is not resolved. I bought this phone recently and get the bad experience.