Whenever I schedule sessions I get more learners by using this tactic: Start off with 5 spots, then when those are filled extend to 10, and so on. This tends to bring more sign ups than having 15 spots from the start. One theory I had was its sort of a brain thing. When people see there are limited spots left(like 1 or 2 since its such a small number) they think I should sign up before its full and clearly since its filling up fast its probably good. Whatever the reason it has definitely helped me increase the amount of learners joining my sessions.