Why would I want to update the iOS on my iPad 2?
The reason that has gotten me finally persuaded to update to iOS 8 was the fact that more and more apps called for mandatory update and would otherwise refuse to run. The one that immediately comes to mind in NFL Game Pass. Also my kids told me that some of the games they wanted to play wouldn't run on iOS 6.

I must say that I was a little afraid to upgrade as I was expecting performance issues on part of iPad 2... I am pleasantly suprised though - there are of course minor lags here and there, but it's not like the update has rendered the iPad unusable - on the contrary. 

So all in all if it's just a matter of preference - it's entirely up to you whether you do it or not, but if you have essential apps calling for the upgrade, I don't see a reason to stay with iOS 6.

I hope that has shed some light on the matter for you.