Well yes, pwede yan. Doesn't matter if 2gb stick + 16gb stick add mo na ram. As long as same sila DDR generation (DDR1, DDR2, DDR3, DDR4), take note sa frequency, if different frequencies ram mo automatically set ng motherboard yung frequently sa lowest na frequency supported by both sticks. Example add ka 2gb 1600mhz ram + 4gb 1333mhz ram, automatic maging 1333mhz sila dalawa for compatibility reasons.