You certainly can, but be warned: many starters haven’t reached their full, glorious bread-making potential before 15 feedings. At that point, a starter is considered “mature”, with a stable microbial community full of acid-producing bacteria and acid-tolerant yeasts that leaven and flavor your bread. Before that, the community is changing daily in a process ecologists call “succession”. Just as a bare patch of dirt will grow grass and weeds, then flowers and shrubs, and eventually a forest (that transitions from pines to hardwoods), the “microbial garden” in your sourdough starter undergoes some pretty drastic changes in its early life. You can “measure” these changes by smelling your starter and recording its height every day. Different microbes perform different functions; so, as the community grows and changes, you will notice that your starter grows and behaves differently, too.
So – if you want to bake with your discarded starter, feel free – but don’t expect a particularly tasty loaf of bread in the early days. (Without a healthy community of yeasts to leaven the bread, your loaf may seem more like a rock cake.) But, in case you’re still interested to compare the bread your starter makes over time, I developed a “tiny loaf” recipe (on page 2 of Dr. McKenney’s easy sourdough recipe) that uses 1 tablespoon of discarded starter.