Both are approx. the same price, but I’m not in the market for two.
https://www.chrono24.com/alangesoehne/a-lange--soehne-1815-updown--id30743598.htm
My wrist is 6.75in, so I think either will work, but the 39mm (1815) probably fits slightly better. I Love the moon complication of the saxonia, but I think I like the overall look of the busier dial of the 1815 as its easier to dress down. I also think the movement displays better on the 1815.
Which would you prefer?