How to speed up old iPad 2 (maybe replace iOS?)
The only practical thing that might help is if your battery is failing - putting in a new one might pep up the processor.

The actual browser is going to be hard to make faster and jailbreaking and running another OS is going to be likely far less optimized than iOS 9 is already for that architecture.

Your main help for browsing websites quickly would be to select websites that don't use javascript much or block that from running and consume text / html / light css.