The weakest point of any building; especially one with 16 foot walls; is the junction where it connects with the ground.
In houses they combat this sheer problem from the wind by skinning the walls with OSB or plywood.
Most pole barns are not built to these standards as a metal skin does not meet the sheer performance.
So the best advise I can give you if you choose to use these options is to use braces; braces; and more braces.
Now with that said......
I live in a area where the water table is just below ground level.
In some places it is above ground level. We call this area a swamp.
We still drive wooden piles under slabs of every house for foundations.
We still build houses 8 feet off the ground on wood pilings.
We still build boat docks where the wood is sitting in salt water 24/7.
And we have none of these post rotting off problems at ground level.
In fact our fence post are more likely to rot from the top down.
Its the reason you see metal cans on top of fence post around here.
Our secret.
We still use CCA treated wood.
I know it may be hard for you to find but at least look for it.
If you can find CCA treated wood treated to 0.80 levels use it.
You will never regret your decision.
It will give you years of service and with solid poles give you the sheer performance.
CCA Pressure Treated Wood