I've had my ZZ plant (Zamioculcas zamiifolia) for about eight months now, and I'm finally seeing new leaflets unfurling from the rhizome

I've had my ZZ plant (Zamioculcas zamiifolia) for about eight months now, and I'm finally seeing new leaflets unfurling from the rhizome. I know they're supposed to be indestructible, but mine's been pretty slow—I'm wondering if I'm underwatering it? I keep it in a cool corner of my apartment and it gets indirect light, so I'm hesitant to water more often than every three weeks. Has anyone else found their ZZ plant slow to establish, or am I just being impatient?