I don't know how to guess, I'd been learning on and off for a long time before I started listening, and I still can't understand all of it fluently. The things I like about their podcast particularly to recommend it is that it's a lot of content - 30 minutes or more at a time and loads of episodes, of consistently good recording quality, it's two people and sometimes a guest talking quite clearly so it's very regular speed and accents to get used to, and they talk about a topic each time so there's quite a lot of repeated vocabulary during one episode, and it's all talking no cuts to music.
