If you are having trouble with ratios, turn them into fractions.
ex; 3 : 5 = 3/5, 8 : 10 = 8/10, 6 : 15 = 6/15
After you have turned all of your ratios into fractions, you can find a common denominator for all the fractions.
ex; 3/5, 8/10, 6/15 ⇒ 3/5, 4/5, 2/5
Now it you can easily order the ratios from least to greatest.
ex; 6 : 15, 3 : 5, 8 : 10