You really don't understand what is being said.
First, your "1.5% of our population is gay" is much lower than most estimates - that is not relevant in this thread.
IF you are looking at total instances of child abuse, combining gay and hetero families - YES, there will be fewer instances of abuse with gay parents. However, to make a relevant comparison, you must look at gay and hetero-led families as two separate categories. Only when you have two or mare categories can you make comparisons. We also must define "abuse". Most often, in a discussion of het vs. homo families, abuse is thought of as sexual in nature but abuse may also be of a physical nature; i.e., instances where a child is beaten and injured, or confined in ways endangering the child, or even in some cases starvation.
To be as fair as possible we must have at a minimum three categories: Straight families, families led by lesbians and those with gay male partners. For a full study, there could be even more categories including economic, education level and racial.
The most recent study I could find, reported ZERO instances of child abuse in lesbian families. Abuse has been reported in almost one-fourth of heterosexual families
There does not appear to be any easily available research on rate of abuse in families led by a gay male couple but other research looking at the children of gay and lesbian couples have found that such kids are at least as successful as those kids raised in a straight family of similar economic circumstances.
Why Gay Parents May Be the Best Parents | Gays, Lesbians & Same-Sex Marriage | Advantages of Gay Parenting & Gay Adoption | LiveScience
Overall, the rate of child abuse is dropping in all classes of families