duke, In addition to Franks explanation of splitting everything up and to answer your question in another way, if you have one plug in that circuit and it's drawing 14 of your 15 amps, you don't have any room for any more plugs.
However, if you have 12 plugs in another circuit with each appliance drawing .5 amps, you'd still have more room for additional plugs/appliances on that circuit (9 amps additional, not subtracting the 80% rule Frank suggested).
So the # of plugs in a circuit is really incidental.
swimmer