My daughter is 4 and is trying to read as much as she can despite not really being able to on her own. Because of that, I try to help her out as much as possible, which isn't a ton because of time. Maybe 15 minutes a night, similar to you.

She has a better time with her other language, Japanese, as that's easier phonetically and she doesn't have to grapple with kanji yet. All letters are come with vowel sounds, with only one exception. I can't help her much on that though, and her mother (the native speaker) also barely has time.