I have three Mac Minis, one with 16GB of memory running OS X 10.10.2, another with 16GB of memory running OS X 10.10.3(beta), and one rather elderly mini with only 8GB of memory. When I open Activity Monitor the "memory pressure" is comfortably in the green on all three of them. Additionally 16GB is the maximum RAM supported on any Mac mini, up to and including the latest one and the memory on the newer ones, like most new Macs, is soldered to the logic board and not upgradeable. All that is to say 16 GB will probably be more than adequate for at least the next few years or more.
