Side-by-side specifications of the Synology DS1515+ and DS1517, from official datasheets. Differences are highlighted.
| DS1515+ | DS1517 | |
| CPU | Intel Atom C2538 | Annapurna Labs Alpine AL-314 1.7GHz |
| Cores / threads | 4 cores / 4 threads | 4 cores / 4 threads |
| RAM (base) | 2 GB DDR3 | 2 GB DDR3L |
| RAM (max) | 6 GB | 2 GB |
| Drive bays | 5 | 5 |
| Expandable to | 10 (with DX513) | 10 (2× DX517) |
| M.2 slots | 0 | 0 |
| Network | 4 x Gigabit | 4× 1GbE RJ-45 |
| 10GbE | no | no |
| Max raw capacity | 30 TB internal; 90 TB with DX513 expansion | 75 TB |
| Hot-swap | yes | yes |
| Form factor | Desktop | Desktop |
| Released | 2015 | 2017 |
| Power consumption | 72.5 W / 18.4 W | 39.5 W / null |
| DSM at launch | — | — |
Choose the DS1517 if you want the cleaner long-term buy: it has a faster Intel CPU, supports more RAM, and is the one with native M.2 SSD slots for cache. It also retains 5 bays and can expand with a DX517, but unlike the DS1515+ it has no built-in 10GbE option. If you need 10GbE specifically, the DS1515+ is the more attractive choice.