To find the median delivery time for each pizza shop, we need to first put the delivery times in order from least to greatest:

Pizza shop 1: 15, 18, 20, 21, 22, 23, 24, 28

Pizza shop 2: 16, 17, 18, 20, 20, 21, 25, 38

The median is the middle value in a set of data when it is put in order. For Pizza shop 1, the median is 22, since it is the middle value when the delivery times are put in order. For Pizza shop 2, the median is also 20, since it is the middle value when the delivery times are put in order.

Based on the medians, Pizza shop 1 has the faster delivery time, since its median delivery time of 22 minutes is lower than Pizza shop 2's median delivery time of 20 minutes.