ARD-LTC1867 shield ADC sampling rate issue

I am currently using ARD-LTC1867 shield from Iowa Scaled Engineering for 16 bit ADC and 200ksps. i managed to get 16 bit ADC but only receiving a sampling rate of up to 1ksps. The attached file is the code that i am using. Please help me with this. Thanks

ADC_v2.ino (1.2 KB)