Whether you have a 60 or 80 gallon TANK - that is still just the tank size - it has NOTHING to do with the compressor capacity!
What you are talking about here is the two times 10 versus 1 times 15 compressors themselves!
So my question back to you would be: Do you have the power available to run 2 motors for the two 10 cfm units?
Second: Are we comparing apples to apples? Are the 2 10 cfm units and the one 15 cfm unit all rated the same way?
And most important - Are they equal in quality?
If all is comparable then what you are asking is "which is better - 20 cfm or 15?"
Tank size is a game played by the manufacturers.