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 |
| Cores / threads | 4-core | 2/4 |
| RAM (base) | 8 GB | 8 GB |
| RAM (max) | 8 GB | 32 GB |
| Drive bays | 5 | 5 |
| Expandable to | 15 | 10 |
| M.2 slots | 2 | 2 |
| Network | 4 x 1GbE RJ-45 | 4x 1GbE |
| 10GbE | no | optional |
| Max raw capacity | 80 TB | 15 drives |
| Hot-swap | yes | yes |
| Form factor | desktop | desktop |
| Released | 2022 | 2022 |
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.