No they’re not the ceasing being that when simplified one is bigger than the other
8/12 simplified is
2/3 because the biggest number that can divide both sides is 4
12/15 simplified is
4/5 because the biggest number that can divided both sides is 3
12:15 is greater than 8:12
You can also find this bu dividing the numerator bu the denominator for both ratios
The biggest number will mean that ratio is bigger