The 224+ has much more power and is authorised for the latest DSM as well as many more options.

Contrary to the manufacturer's recommendation, you can install more RAM. I currently have a total of 10 GB available. With photos, this is useful due to the faster calculation of preview images. For videos in connection with PLEX (client-server media playback system), the calculation time for playback on the TV is much shorter than with my "old" DS715. We mainly use the server to store all our photos and videos. Whether the source is a mobile phone, digital camera or scanned slides or photos. The mobile phones are automatically synchronised with the server. With the DS715, the RAM utilisation was always more than 90%. With the DS224 it is now 21%. However, it was security that persuaded me to buy a new one. The DS715 is no longer supplied with updates from Synology. The latest version of the DS715's operating system is DSM7.1.1, while that of the DS224 is 7.2.1. This means that important, security-relevant updates for the DS715 are no longer provided by the manufacturer. The risk of being hacked because we operate a private server that is connected to the Internet was simply too great for us.

More performance. This is noticeable when you open photos or videos, for example. I don't know whether you can also use the new operating system on the current one. If you simply store Nordstern on it, it's not worth the investment. But if you want to use it, it is.