I haven't done anything special.
Originally Posted by msadat
Hardware: Mac mini mid-2012 computer with i7 Quad-core, 2.6Ghz and 16G RAM; internal 950G Crucial SSD. Apple Thunderbolt Display 27". External 2T working drive connected via USB3.
Software: latest macOS El Capitan 10.11.6. Lightroom 6.5.1 or 6.6. Lightroom catalog on the startup drive, image file repository on the external working drive. Camera Raw Cache = 10Gbyte. Free space on startup drive = 250Gbyte.
A simple test: Exporting 63 randomly selected Leica SL raw files to full resolution JPEGs files took 3.12 seconds apiece, a total of 3 min:16 sec.