Of the original 16 velocity layers, only 3 are used, making the library around 300MB while the original is over a gigabyte. The intermediate velocity layers are simulated via velocity crossfading which is the purpose of the phase alignment.
The sample library uses the SFZ format.
Download links can be found at Musical Artifacts:
44 kHz 16 bit
https://musical-artifacts.com/artifacts/534
48 kHz 24 bit
https://musical-artifacts.com/artifacts/533
More info here:
http://sig-ex.com/2017/11/11/slender-sa ... and-piano/
Enjoy!