Home Office Systems cannot be interrogated in a way that will provide any meaningful response to the question. A manual review of all applications submitted within the stipulated timeframe would be needed in order to provide an accurate response and this would incur a disproportionate cost to the public purse.
Therefore, the average length of time taken to determine a second or subsequent further leave to remain application made on the basis of (1) family, and (2) private, life in (a) 2015, and (b) 2016 cannot be provided.
The versions for previous years are available here:
These tables have also been attached to this answer.