Not only is preaching not a requirement to qualify for baptism, but, contrary to what Watchtower teaches, the work of active formal evangelizing is not even required of all christians!
And he gave some as apostles, some as prophets, some as evangelizers, some as shepherds and teachers - Ephesians 4:11
JWs treat qualifying for baptism as if it were passing your college exams to graduate from college. But in reality, qualifying for baptism is more like meeting the basic requirements to enter into college.
When you look at the NT it is clear that one only needs to know the good news about Jesus, repent, and exercise faith in him to qualify for baptism. They grow in knowledge and understanding and mature further, after they're already baptized.
Something else about JW baptism that is clearly unscriptural is the long delay that candidates have to wait between qualifying and actually being baptized. The scriptures show that those who qualified were baptized teh same day that they were convinced. (Acts 2:41; Acts 8:36-38; Acts 10:44-48; Acts 16:33; Acts 22:16) The NT indicates that those who qualified were baptized immediately, without delay. Peter didn't even wait for Cornelius to resign from the army before baptizing him! JWs let baptismal candidates wait up to 6 months or however long until the next assembly or convention, before being baptized. The urgency of the person's salvation has to take a back seat to gloating and grandstanding over new recruits at the convention.
Imagine a scenario where a person is qualified to be baptized but he obeys the elders and the organization by delaying his baptism until the convention. But the end comes before the convention! Jesus says to him:
"Why are you not baptized?"
Person: "I already qualify and would be - would have been - baptized at the upcoming convention but the ... you ... have intervened. But I'm already dedicated and that's the most important thing, right?"
Jesus: "Why did you not get baptized without delay as soon as you qualifed?"
Person: "That's not how its done in the organization. The person has to wait until the next assembly or convention"
Jesus: "Did my faithful Witness, Cornelius, wait until the next convention? Did you never read of what Candace's attendant said to Philip when he qualified: "What prevents me from getting baptized?" You let men prevent you from getting baptized. You have shown greater affection for elders and for organization than for me. You are not worthy of me. Depart from me, you cowardly follower of men! To the lake of fire with you! There is where your weeping and gnashing of teeth will be."