Thank you for your interest in our gearmotors. Unfortunately, we do not have our motor or gearbox lifetimes well characterized, and in general, the lifetimes can depend on many different factors. What kind of lifetimes are you looking for and under what conditions?
A general rule of thumb for brushed DC motors is to limit continuous operation to around 25% of the stall torque/current. You can probably safely do a little more than this for lower-power motors like the version you are considering, but I am still a little concerned about continuous operation at 50% of the stall current.
Your target of 1500 hours sounds high to me, especially under the conditions you have mentioned, but that’s based more on feeling than any tests we have done. (For some kind of rough reference, we have been running some of our 99:1 25D 6V HP gearmotors continuously at no load, and they are currently approaching 700 hours, but it’s hard to extrapolate this to a different motor winding and gear ratio operating under substantial load.) Ultimately, I think if you want to get some sense of the lifetime, you will need to test the motors yourself under your expected conditions. Perhaps you could accelerate things by significantly reducing the rest period? If you do test it, we would be interested in hearing your results.