Side-by-side specifications of the Synology DS1515 and DS1515+, from official datasheets. Differences are highlighted.
| DS1515 | DS1515+ | |
| CPU | quad-core CPU | Intel Atom C2538 |
| Cores / threads | 4 | 4/4 |
| RAM (base) | 2GB | 2 GB |
| RAM (max) | 6GB | 6 GB |
| Drive bays | 5 | 5 |
| Expandable to | 15 | 15 |
| M.2 slots | 0 | 0 |
| Network | 4x 1GbE | 4x GbE |
| 10GbE | no | no |
| Max raw capacity | 40TB | 30 TB |
| Hot-swap | yes | yes |
| Form factor | desktop | desktop |
| Released | 2015 | 2015 |
Choose the DS1515+ if you want materially better performance: it uses a much faster Intel C2538 CPU and supports a higher RAM ceiling than the DS1515’s Annapurna Labs chip. Both are 5-bay units with the same 2× eSATA expansion support, and neither has built-in 10GbE or M.2; between them, the + model is the decisive pick for SMB use.