Factors such as traffic, red lights, hilly terrain, wind, overall weight of the load and your personal riding style/training level will affect average speed, which can also vary from one ride to the next.

My commute is urban/suburban, "hilly" terrain, carrying several pounds extra load. My 14 to 15 mile trip takes about an hour.
I never expect to go any faster.

Although I often take "the road less travelled" to avoid congested traffic in the afternoons, one of my favorite joys is to
take a congested artery instead. I love passing long lines of crawling traffic. It's my way of saying "Nya-nya-nya-nya-nya!"