Hi Cossack
Recent ex Heathrow/Gatwick ATC. Genuine question, not a willy waving comp.
What is your latest DME range to issue landing clearance in low vis? At Heathrow and Gatwick, it is 2 miles (any preceding landing must have passed the CAT 3 bar, or departure must have passed overhead the localiser) with the option of continuing to 1nm if certain conditions apply.
As I remember, we would commonly do about 24-28 total in low vis off Gatwick's single runway; 10nm between arrivals, 1 departure in the gap. 15nm seems large (ish) to me, we'd want to get two away in that but perhaps there is a specific reason for that? (X2 would be up to about 56.)
At Heathrow (twin parallels, segregated) the normal low vis spacing is 6nm, giving about 26 arrivals and also about 40 departures p/h; 66 total. Still a clear advantage for segregated ops. but perhaps not so much as with you.
You do "crossover" on departure?? Does the track structure spread well immediately after departure to give climb and vectoring space?
.4