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/RIMLPAAAR_N.M, is available at:
http://www.federalreserve.gov/datadownload/Output.aspx?rel=H15&series=1d4deed1b60dba46ea77c562e3c472cd&lastObs=&from=&to=&filetype=csv&label=include&layout=seriescolumn