How many users on Mac Mini Server?

Good morning,

Apple's recent changes to the Mac Mini line have thrown a wrench in a project plan I've been working. One part of the project needs a quad-core computer (FileMaker Server) and so I'm having to either search for an older model or switch up to a Mac Pro.

The other part of the project involves bringing a Mac-based server in for directory and user services, including mail. I had planned to use the high-end Mac Mini Server but that option was removed. The office I'm supporting is about 15 people (usually a little less on the network) and most of their work will actually be done against the other computer running the FileMaker Server-based application. I was not expecting a big load against the Mac Mini Server. But these changes got me wondering, what are others' experiences with Mac Mini as a server for 12-15 people? I'm happy with qualitative and quantitative data, but I would like to know which is which. In general:

For how many users have you provided directory and user services (built in to the OS) using a single Mac Mini?

What were the specs of the Mac Mini (year or model, speed, CPU config, RAM)?

Other thoughts?

In essence, I need to understand if people have successfully used dual core processors as Mac Mini servers in environments of 12-15 people. I've done it using a 2012 Mac Mini Server with 5-6 and the loading seems to support further growth, but would like real-world experience.

Thanks.