Yeah i have a 50 acre one that came out very nice but like you have learned it is a huge file and eats up a lot of RAM when it is loaded into a program. First impressions are everything, this is where a composited video presentation showing off features, like your maps and models may be a good compromise for your first encounter, as you most likely are using something you mapped prior to this and not a job for that company. They really only need to get a sense of what you can do, what competitive advantage that can provide them, and what kind of producibles you are capable of. Then if they would like to see more you can get them a .obj file that is a bit more manageable.
Getting some base level 3d knowledge is helpful, but you could also find some 3D modelers /CAD that can do that end for you for a fee.
The developers are good at working with other API and they may be in the process of better skecthfab integration as we speak, if not sure makes a good feature request. My 3D knowledge comes directly from my experience with video games and development, luckily it is all essentially the same so the knowledge transfers nicely.