Kitade-san who is one of the FFXV programmers wrote a message on the Japanese side of the forum to explain a little bit more about the pre-beta stage of developement. You can read the original message in Japanese here and below is the official English translation
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Nice to meet you all, My name is Kitade Satoshi and I am a programmer. I am mainly responsible for maintaining the development environment for FFXV. Today I would like to explain some more about the pre-beta version of the game that we talked about on Twitter a little while ago.
The term “pre-beta version” refers to the product of development on FFXV that was put together in October this year. We have managed to achieve two things with this pre-beta:
1.) We have managed to get the game in a state where you can play the whole thing through from the opening to the ending. By doing this, all the dev. staff are now able to get a shared impression of the overall game.
In short, we can now say that we have done the groundwork for finishing all the different areas of content in the game and the overall product itself to a high standard, polishing up each individual element and fine tuning the gameplay.
There are mechanics and elements that are still undergoing testing and are not implemented in the release code yet, but making it possible for all the dev. staff to grasp an overall image of the game is very important for the next stage of the development process.
As a programmer, I am now in a situation where I can concentrate on the process of optimization and will be pulling out all the stops to get the appeal of the finished product across to people as much as possible.
2.) We have polished the first half of the game to final retail quality and established the final feel of the gameplay.
By doing this we have been able to extrapolate how much work will be necessary in order to bring all aspects of the game, including the feel of the gameplay and the standard of the visuals, up to the final quality level we envisage.
At the same time we have been able to check how actual players will approach playing the game and the pace of their play by inviting valuable players from outside the company in for focus testing.
We have entered the final phase of development now, where the technology and people’s feelings and intuition come together, and this is where the programmers can really show their stuff. You can expect great things from us!
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One thing to note is that game development is very complicated and there's still quite a lot of work needed to be done on FFXV but the team are making good progress
https://forum.finalfantasyxv.com/discussion/816/development-info-about-ffxv-pre-beta#latest
From the official FF15 website
Kitade-san who is one of the FFXV programmers wrote a message on the Japanese side of the forum to explain a little bit more about the pre-beta stage of developement. You can read the original message in Japanese here and below is the official English translation