The 15 Heliar has electronic communication to the camera ? I have used the old 15/4.5 for F cameras through a nice F-Z adapter, and the solution is extremely compact and light weight, but prone to severe vignetting. What about the new design in that respect?
I just got the Viltrox 16mm f/1.8 for my Zf, and it is an excellent performer, but rather heavy.