With an 800 MHz CPU and 256MB RAM, the technical specification is the same as the DS214se launched at the beginning of the year. Although we haven't yet had the opportunity to take one apart, we rather suspect it may be based around the same motherboard.
Like the 214se, there are some strange omissions. For instance, the ports are USB 2.0 specification rather than USB 3.0. In order to use a 2.5" hard drive, an adapter bracket has to be purchased. And if it is the same innards as the 214se, there is no support for scheduled power on/off or Wake-On-LAN (WOL). Whilst this helps minimise the price, it reeks of penny-pinching and can only be saving a pound or two. Still, the DS115j is a worthy successor to the DS112j and a great first NAS for many people.
Update: a video of the DS115j being unboxed is now on YouTube at:
https://www.youtube.com/watch?v=XLX_iJOSI8c