Reduce preview size

Is there a way to reduce preview size. I have tried the 3 different rendering quaities under color mgt. I still find it shocking at in a 3.94 gig session that 1.47 gigs are previews. When I archive the jobs I don't add the previews , because on bigger jobs that I shoot the sessions are upwards of 30-50 gigs using my Canon's or P25.
Brian