Development of version 1.5 is still fully in progress, but already patch 1.5 contains many more changes than any previous patch. These changes fix bugs and make some small improvements. We'll release both a full version of 1.5 as well as a 1.5 patch that can be applied to any previous version. Saves from previous versions most likely won't be compatible with new version, though. This means that saves from version 1.4 won't load in version 1.5. But I think that with so many changes, it makes more sense to play the game from the start.
My guess is that version 1.5 will be released some time this November. For now, it isn't possible to give you a better time estimate. We'll no doubt let you know before its release, when we'll be able to determine a concrete release date.
One example of small improvement for version 1.5: Some of the players didn't notice imperial army lieutenant Terrak in the Wild Paradise. He's an important character because by talking with him, a quest line concerning the Anonym starts and the player gains access to the Imperial City. So now when the player asks the barman about the patrons of the Wild Paradise, he'll mention Terrak along with the others, and the player can then ask to learn more about him.