Okay well, this thread was made back in 2018, so I'm assuming the earliest version dates back around then. Maybe released sometime in 2017 and ended up here a bit later. Current version is the finished version of the arena, either June or July of last year - it's basically a prequel and tech demo for the main game to come.
I'm assuming you're new to Bio, so... We're waiting for this month's supporter news update to either hear how far along the first version release is, or to guess how far if it's not explicitly mentioned. They're making the main game in Unreal 5, and integrating the systems and (mostly the) animations from UE 4 to 5 has been the biggest hurdle for time they've said.
The main game will have episodic updates, so 1 chapter or level at a time (maybe 2 if we're lucky). Don't quote me on that, it's just a personal hope. They've also worked on a randomization system for enemy type appearances, and a sort of modular outfit customization where we can choose different combinations of outfit items, so this should mean you could equip the top, bottom and footwear each from different outfits. Or wear the holster with whatever, or no holster on any outfit - footwear as well. In the arena, outfits are entirely preset and can't be changed, so for that example, if you like the shoulder holster like me, you're SOL in the arena because it's only part of 1 outfit.
As for reducing the size of the game which is what I'm assuming you mean by shortening the megabytes... I don't think there's any other way to outside of being able to modify the source game files in Unreal and completely rebaking it as if it were a completely separate game. Which I'm not even sure is possible with the versions they release.