It depends on the nature of the quantization of the gravitational field. If we expect the gravitational field itself to be quantized in a manner somewhat similar to the electromagnetic field, we may be able to detect quantum effects without the objects being particularly small. A good analogue is the photoelectric effect, which involves no superposition at all and can be observed even with macro amounts of energy involved.

Not sure if this has held up, but Google points at this 2010 paper that put a microscopic object into a superposition: https://www.researchgate.net/publication/232755709_Quantum_g...