I don't think it's quite that big. In one of the trailers it shows the circle that the dreadnought made in the rings, this circle is something that can't be more than 1/15 of the diameter of the current rings diameter just bassed on eyeball observations, and the dreadnought itself is at most 1/3 of that 1/15 in its length, so I'm thinking something closer to 1622 kilometers. Edited because I forgot it was in KILOmeters.