The H.15 historical data is available through the Data Download Program at:
http://www.federalreserve.gov/datadownload/Build.aspx?rel=H15

This series, H15/H15/RIFSPFF_N.BWAW, is available at:
http://www.federalreserve.gov/datadownload/Output.aspx?rel=H15&series=8c1d89de04e1e5d27f9c9da4c64f8ef8&lastObs=&from=&to=&filetype=csv&label=include&layout=seriescolumn