Side-by-side specifications of the Synology DS1520+ and DS1522+, from official datasheets. Differences are highlighted.
| DS1520+ | DS1522+ | |
| CPU | Intel Celeron J4125 | AMD Ryzen R1600 2.6 GHz, up to 3.1 GHz |
| Cores / threads | 4 cores / 4 threads | 2 cores / 4 threads |
| RAM (base) | 8 GB DDR4 non-ECC | 8 GB DDR4 ECC SODIMM |
| RAM (max) | 8 GB | 32 GB |
| Drive bays | 5 | 5 |
| Expandable to | 15 total (2 DX517) | 10 |
| M.2 slots | 2 NVMe M.2 2280 | 2 M.2 2280 NVMe |
| Network | 4 x 1GbE RJ-45 | 4 x 1GbE RJ-45 |
| 10GbE | no | optional |
| Max raw capacity | 80 TB internal raw; 108 TB maximum single volume | 15 drives |
| Hot-swap | yes | yes |
| Form factor | Desktop | Desktop |
| Released | 2020 | 2021 |
| Power consumption | 52.06 W / 16.07 W | 52.06 W / 16.71 W |
| DSM at launch | 7.0 | — |
Choose the DS1522+ if you want the newer platform: it uses a Ryzen CPU, supports up to 32GB RAM, and can add 10GbE via an expansion card. It also keeps 5 bays and adds M.2 NVMe slots for SSD cache/volume use, but still has no built-in 10GbE and no major bay-count advantage over the DS1520+.
Choose the DS1520+ only if you can get it cheaper; its Intel Celeron CPU, lower RAM ceiling, and older platform make it the less future-proof pick.