I made a detailed video going over my 25 Halo Maps I made between 2005-2007 and in that video I returned to map making in 2017 to make one final (26th) map, 10 years after my last map was released: https://www.youtube.com/watch?v=wiS9v4QGAcg
Full map is just over 11,000 polygons which is the suggested limit for Halo: Custom Edition levels, the side tunnels/interiors have portalling in place to optimize performance.
Arrival - Halo CE Map Trailer [Unlisted]