For info, the tyre size is a mixture of metric (mm) and imperial (inch) vcalues and decomposes as follows:
225/60/15
225 mm wide
15 inches (wheel) diameter - the inner tyre radius.
60 - a percentage factor of the height of the tyre compared with the width of the tyre.
There are many interactive tyre size calculators on the web, eg:
http://www.miata.net/garage/tirecalc.html
As stated, changing from a 60 % to 50 % aspect tyre won't feel greatly different. You *may* notice a more communicative ride, feeling the road a little more but I doubt I could tell the difference.