The CEFR seems like a great reference point though that I wasn't aware of so that could be a great more objective measure.
We're hoping to add a few shows/ podcasts to our regime this summer to get our ears more accustomed.
That's at least what is helping me with Swedish.
Realistically if you want to get to at least a B2 level you are going to need much more than 15-30 min daily, even more because you aren't immersed in the culture and German is, frankly speaking, a quite hard language to learn. Sentence structure looks quite foreign if you only know English, grammar is complex, you have 3 different genders, etc.
Not trying to discourage you, much the opposite, go harder and you can do it but be realistic about it.
Try to focus on shows/podcasts that target children and/or teens -- the language will be more at your level. There may be more slang, but that will be relatively simple to navigate via various language forums.
Once your ear gets tuned to listening to native-speed German, then you can move on to more adult-oriented topics (start with simple, fun stuff and then move on to material that covers "real" topics).