15 grams of instant yeast is a small amount that measures 0.529 oz (15 g) by weight. It occupies 1.84 tbsp (27.3 mL) of space, which is about the size of a ping-pong ball.

In kitchen measures
1.84 tablespoons
5.53 tsp · 1.84 tbsp · 0.115 cups
about the size of a ping-pong ball
Instant yeast typically ranges 0.5–0.62 g/mL depending on how it's packed. A firmly packed scoop weighs more.