I just googled it (in case you have not) and one site says that there are several of these routes. That if you do the just the Camino de Santiago Frances to Camino de Santiago Compostela you would have to walk between 14-16 miles per day for 30 to 35 days. Just go to www.google.com
and type in Camino de Santiago, you will bring up several sites on it. Lots of good information easily found.
Hope this helps