Should I upgrade my iPad 2 to iOS 9.3 from iOS 5.1.1? ( Late March 2016)
This Wikipedia Page states that "Although the A5-based iPad 2 is relatively archaic, showing signs of its age in iOS 8, iOS 9 is said to feature performance improvements that may help the aging device function more smoothly, and initial tests suggest that it did not significantly impact available space."

I upgraded three iPad2s last week, and did not notice any degradation in the short time I had for testing. I was making sure that they could be managed by our MDM and that a small set of common apps we use worked.