I think I see what you see in this model. I particularly like the pink gold base at the cannon pinion which is unique to this piece - and certainly to the 1815 line.
I owned this exact reference for several years - but I released it when, as much as I loved it, I had to be honest with myself that I could no-longer read the sub-indices. Though an annual calendar not a perpetual calendar, it reminded me of the old saying that "by the time you can afford a perpetual calendar, you can no longer read one".
I miss it, but I have retained the three-hand 1815, and the 1815 Up / Down - both in pink gold - to console me and scratch the irresistible and charming 1815 itch.