Hi Bunky! Just a couple of things to consider. First, changing to 15 inch wheels simply involves paying for them and having them put on. You should be aware, however, that the ride will be noticeably harsher since the tires will have a lower aspect ratio (I think you go to 55 from the standard 65). My choice would be to switch to a better quality tire rather than switching sizes. You will wind up with at least as go ride, better handling than standard, and much lower final price than with switching to 15s. A lot of people like the looks of the larger wheels though. Who told you to switch tires and why?
The other question is, are you aware that the new ECHO is due to come out sometime between late July and November, depending on who you believe. From what I can tell, the interior should be much improved, the wheelbase is longer by about 4" (a mixed blessing in my eyes), and in general, it is said to be a more sophisticated car. I intend to wait for it (praying that my current beast holds together that long).