Hi,
On Copernicus, Sentinel Level 2 data is only available starting from March 2018. Anything before that, only Level1 is available.
I have seen a post here where I understand that sentinel hub is processing all historic Level 1 data through Sen2Cor so that all equivalent Level2 data will become available. Is my understanding of this correct?
Will Level 2 data between 2015 and March 2018 become available soon - and if it is already - does it include this entire time range?
Your understanding is correct. In the post we also state the time range of the data availability… It is planned to go back to 1.1.2017, for the moment available back to 1.7.2017.
Is there a plan to push that back even further and get all L1 converted, since L1 data started to become available from 2015?
Not at the moment.
The current version of Sen2Cor does not work nicely with old version of the product (.SAFE vs. .SAFE.compact) so there would be too much of effort required. Plus there is not that much data then anyway
Is there any ETA on when L2A will be back processed to Jan 2017 instead of July 2017? Very eager for the data! 
We do not have an ETA yet, but should be competed over summer. We want to do some thorough analysis first in order to get best possible results.