Yes, Empfindlicher Kopf Zuender may even be a better possibility. But, if R doesn't stand for Rocket, what could it possibly stand for ? I just checked my archive. I'm shure that R stands for Rocket. This 15cm shell is the one with which all the trials with the electric fuze have been done. The name of the shell is "R.-Gr. 19". It's length is 804mm compared with 615mm for the normal "15cm Gr. 19". The firing distance for the rocket assisted shell was 19000m. Because of the ionised gas of the rocket exhaust they had big problems with the "El.A.Z." fuze and then the "El.A.Z.m.B." was developed. This shell was never really introduced also about 25000 were manufactured. It seems that this "range extended 15cm shell" was used extensively not only to test electric fuzes, but also the above shown fuze. Another fuze, which worked apparently satisfactory, was the "Bd.Z.R."="Base Fuze Rocket(assisted)" which only ignited the rocket propellant. For ranging shots with earial bursts the "Dopp.Z. S/90" was used. Another fuze for this shell is the "K.Z. 28 P"= Kopfzuender 28 Pressstoff. To get an idea what this shell could do, here some data : range 18200m, flight time 68,3 sec, final velocity 322m/sec, dispersal: 224m length, 40m horizontal and 390m in height. The shell was fired with the 8th charge and had a muzzlevelocity of 505m/sec with a shell weight of 45,1 kg.
Regards,
Bellifortis.