If you want a quick automated solution, you could try our online optimizer. It's like Simplygon but better (imho). https://rapidcompact.com You get a bunch of free credits per month, as a try-before-you-maybe-buy kind of thing. CAD presets, customizable, etc. That said, for up-close in-game use I'd still go with Alex_J's…
i think you'll likely end up wanting to break it down into reuseable pieces so that only things local to the player can be loaded as needed and also so you benefit from instancing, however since you already have complete models that are organized a certain way, I think it wouldn't be a bad idea to drop those in your game…