Less than 20 years for sure.
Under the German penal code, Strafgesetzbuch, there are two sections relating to murder:
Totschlag[1], § 212, “intentional killing”, is punished with five to fifteen years in prison,
[2] Mord, § 211, “murder”, is used only if the case is especially severe:
...whoever kills a human being out of murderous intent, to satisfy sexual desires, out of greed or otherwise base motives, insidiously or cruelly, or with means dangerous to the public, or in order to commit or cover up another crime...”
For Mord the penalty is lifelong imprisonment - although usually suspended after 17–18 years.