Comparing a Nougat 7.1.1 ROM from February 2017 with a current build clearly shows you that the older one runs much faster. This is mainly noticeable when scrolling or if you open apps. In the current ROM there are often lags, it simply needs more performance.
To get the maximum out, a few tweaks with a modded Kernel Adiutor from XDA are necessary, the CPU frequency is set to minimum and maximum 1200 MHz. The battery drain of course is a bit higher - not much, but you have more joy with a smooth running S2.
What do you need for this?
I did made the best experience with AICP 12.1 ROM, build in February 07 2017. you get it here. It runs very stable for daily usage. Only the camera app Snap.apk is buggy at video recordings. You can change this by installing the latest one in my attachment.
The modded XDA Kernel Adiutor is attached too.
The CPU and ondemand governor settings (CPU Governor Tunables) you see on my screenshots. Make sure that the "Apply on boot" toggle is set to on.