You are allowed to modify the support order, regardless of circumstances, every three years. Since it was last done in 2001, you should be good to go.
Does the 15% change in circumstance rule apply only to income or can it also apply to changes in the cost of living? When my divorce was final in 2001, I was awarded a small allowance for gasoline, since I was obligated to supply all costs for vistation transports. We all know what gasoline prices have done since 2001. They have almost tripled. Not only that, I carry the health insurance premiums and the life insurance premiums, both of which have gone up since 2001. My income has been about the same, but these court ordered expenses have risen dramatically. Is there hope that this would be considered should I wish to file a motion to modify suport?