The best description of Tea Cake’s intent in mentioning Janie and Mrs. Turner to Mr. Turner is: He wants to show Mr. Turner that Janie works harder than Mrs. Turner.
In this context, Tea Cake is contrasting the work and responsibilities of Janie with the leisure of Mrs. Turner, implying that Janie's life is more demanding and she has less time for social visits. This serves to highlight Janie's strength and commitment, as well as possibly to create a point of connection with Mr. Turner regarding the differing dynamics in their respective marriages.