First of all Network slicing is the key feature of the 5G networks & enables to build dedicated logical networks on a shared infrastructure.
And to respond to the question, Yes, Network slicing is defined from Rel15 and can be implemented in network products. However, we should consider that only simple slices configuration can be deployed with Rel15, and not the more complex scenarios (dynamic slices, etc). That will come with enhancements in subsequent releases.
On the RAN side, Rel15 provides the main building blocks to implement the most important features on slicing (slice aware admission control, scheduling, mobility…).
Some enhancements are planned in Rel17, mostly on mobility, with cell selection, slice remapping, fallback, to ensure smooth continuity of slices across wide area networks.
