How to make a series that has all of the data on a secondary axis?

It is not clear to me exactly what you're trying to do.

If you want some of your data to be on the primary axis system and some of your data to be on the secondary axis system, you will need separate data series for each. If I assume your spreadsheet currently has two columns (one for 2015 and one for 2016), you will need to expand to an additional four columns (2015 primary, 2016 primary, 2015 secondary, 2016 secondary). Populate these four columns with the desired values for each entry, then base your chart on these four columns. Use the format series dialog to transfer the desired data series to the secondary axis system.

It's a little more complex to build, but a panel chart might be a better overall technique for visualizing data like this: http://peltiertech.com/Excel/Charts/StackedCharts.html