How long can a cellist reasonably sustain a tremelo?

I've been asked to write a string quartet, and unfortunately strings are the group of instruments with which I have the LEAST personal experience (being a woodwind player myself). This being said, I do have at least a little working knowledge and a pretty solid idea for the piece, except I want the cellist to do single 16th note tremelos at Quarter = 128 for quite awhile it seems. Is this feasible in terms of stamina or should I find another solution for the sound I'm after?