Where's Dave?... he's the resident expert on this... ...
...anyway,.. I'm gonna' say 14" is really, really pushin' it...
I have 12.5" on mine... I know some have gone to 13"... but I never heard of going to 14"...

Why do want it so long?... (if you want seat height, I'd go 13" and then look to raising the seat,... because our short swingarm will start getting radically jacked and you'll also be needing excessive chain/belt slack,..brake linkage might give some problems too)...

Here I am.....I was out cutting and splitting firewood.  All of our Ash trees have been killed by the Emerald Ash Borer.  They take forever to clean up the mess after you drop them....the brittle limbs and twigs just explode when the tree hits the ground.  The debris field is incredible!

There are two problems going with that long of a shock.  One is the swing arm becomes really angled, and it would be hard to control the belt tension.  If you tightened the belt sufficiently for normal riding, it would become too tight when the shocks compressed.  The other problem is that you might be rubbing the belt on the swing arm pivot point....not sure about that one.

I think the 13" length is about as long as you can go.

Dave