it is very stressful for fish to be put into a new tank (whether they are the first inhabitants or they are being added to an established setup). big water changes may be kind of stressful at first depending on the fish, but the fish will very quickly learn the routine and even eat during the water change. i would work my way up to 75% if they're not used to it. if they are used to 25% weekly, do a 50% one week and then a 75%, dont just jump from 25% once a month to 75% a week.