2.5D integrated systems exploiting electronic interposers to tightly integrate multiple processor dies into the same package suffer from significant performance degradation caused by the large latency overheads of their die-to-die multihop electrical interconnection networks. Silicon-photonic interposers with wavelength-routed interconnects can overcome this issue by enabling directly connected, scalable topologies while exhibiting low-energy optical communication even at large distances. This paper studies the use of an arrayed waveguide grating router (AWGR) as a scalable, low-latency silicon-photonic interconnection fabric for computing systems with up to 256 cores. Our results indicate that AWGRs could be a key enabler for large-scale interposer systems, offering an average performance speed-up of at least 1.25× with 1.32× lower power for 256 cores compared to state-of-the-art electrical networks, while offering a more compact solution compared to alternative photonic interconnects.