Hi, I have done nearly 40 interviews in total (social sciences), with participants being divided into several sub-groups. Although this is a few more than you intend to do, I have a few publications based on specific aspects of my thesis, and therefore only one or two sub-groups were referred to (as the other participants were not relevant to the article, if that makes sense). So, as an example, one of my publications is based on interviews with 9 participants, and this was fine for publication :)
So basically, yes I think 20 will be fine as long as they are in-depth interviews, and you justify the reasons for (what may be deemed as) your 'small' sample size. I think 20 participants is a rather large sample though if it is a qualitative study you're doing. I can't imagine that it would be a problem for publication.