Sometimes it is easier to ask for forgiveness than for permission.
If you have it protected from public use, and it is being used so lightly that it creates no burden on the server, then it is unlikely you will hear anything from DreamHost about it.
If it does create a burden on the server (and it most certainly will if left available for public use), even with only "15 people", you *will hear about it!
Note, this is only my "general advice" and I do not speak for DreamHost. If you want an official answer, or an answer from DreamHost, you should post the question as a support ticket.