Guided Tours Israel group size?

I'm looking at a couple different tours by Guided Tours Israel. The group can be as small as 6 (but at 8+ you get a driver and a guide) or as large as 16 for the same cost per person. Although this is still much smaller than many tours, how much of a drawback is a group of 16 compared to 8?

I'd appreciate the input from anyone who has used GTI, especially if you have experienced both ends in size. TIA! :)

Not sure if you've already been on your cruise, but we had a group of 6. We were in a minivan. Our driver/guide was an Israeli transplanted US. We did an overnight in Jerusalem.