Yes, what you want to do is possible. If your water is of good quality (no particulates, no iron, reasonable TDS and pH, no turbidity/tannins) the softener can be allowed to go longer between regens and no reprogramming will be necessary when you add to your family. If there are some other issues with your water, then the softener can simply be programmed with a shorter override time and regens will happen based on time rather than hardness until you add to your family. Either way works.

Water analysis is necessary for proper sizing in either case. "About" 15 grains isn't adequate information. Pull your city's water report (it may be available online) and post the results. You may need additional analysis as well. You need: hardness, particulates (iron/manganese content of particulates), TDS, pH. In addition: Does the water have any odor or color? Are there any water issues specific to your city?

Thank you for the reply Alice. Below are the stats you requested. My water doesn't have any color, but it does have a strong chlorine smell and doesn't taste great. With that said, I'm also thinking about getting a carbon filter. I'm trying to choose between a bigger upflow unit ($400-$500) or a big blue canister with a carbon filter. Thanks again!

Hardness: 250 mg/L
Iron: Manganese: TDS: 530 mg/L
pH: 8.2 unit