Don't get the sids, they're an investment that shouldn't be made JUST because of the snails. And it has already been mentioned that they are not great snail eaters. They're very active and would probably not do as well in a 10 gallon, although it is possible. I feel bad keeping them in a 15, granted the extra footprint makes a difference. There's no sense in getting a fish only to do a job that can easily be controlled and then stick them in a tank where they will not thrive.
If you are keeping the zebras in the long run they need more than just the two of them.