The real question for me is where to put the arm & leg warmers and vests when the ride temps here in south Florida go from the low 50's to the upper 70's. We make extensive use of an expandable trunk.
A picture of a new Calfee 2 seater recently made the rounds with a reputed weight of 21 pounds, but I don't recall seeing any of the light weight tandems with a trunk. I'm not even sure it's possible to mount one.
15 pounds would sure help when we (attempt) to ride with the big dogs.