30x950x15 is a good size for the stock wheels. 235x75x15 is a little smaller but look good on a stock Sportage.
Like you said 215 is the width in mm. 70 is the aspect ratio. To find out the height of a tire here is a formula. It is not excact because the tire manufactors are all differant. I will use your 215 for and example.

215 x .70 / 25.4 x 2 + 15 = 26.8

215 width
x
.70 sidewall heigth
devided by
25.4 converts mm to inches
x
2 sidewalls
+
15 wheel size

like I said this isn't excact but it will get you in the ballpark.
Dennis

95 Sportage, gone but not forgotten.
98 Jeep TJ, 4" Zone springs with RC Long arms, Ford 8.8", 4.56 gears & Detroit locker rear, D30, 4.56 & Detroit Trutrack front.