You should be able to do this although it will affect your handling and your speedometer a small amount.
Can I Mount P205/70/r15 On P215/70/r15 Rims?
Yes as long as you have the clearance on your fenders and struts! The tire tire you are suggesting to put on those rims will only need about 1/4" extra clearance! They are a little taller and wider than the old size! They will also make your speedo 1-2 miles per hour out of sinc.
