Is there a better way ( for faster read/ write ), to boot instead of using the microSD slot?
Only the Raspberry Pi 3 can boot from USB pendrives and harddisks. This is not always faster , but might be more stable since consumer harddisks are not worn down as much by many small random writes as consumer SD cards.
You need to insert an SD card once to enable USB Boot !
Check the official USB Boot instructions here.