It's been a very longtime, but you could start with Part II I suppose, as you should begin that new adventure with a level 1 PC again, meant to be the successor of the Part I hero.
I don't remember any major difference between the two parts, and considering the latest one being often better than the earliest module, because of the "builder skills improvments"...
And both are very very long modules, so...
I would always recommend to play any serie from its very start, even prologue, but this one might be one of the few exceptions.