Not usually. Low red blood cell counts are not typically determined by age. It is best to first find out if it is low compared to all 15 month olds or low for your child.
No. Low Red Blood Cell count in anyone is not considered normal. If you are concerned about this ask your child's doctor about the causes and the potential risks of this issue.
No. It is not normal for anyone, particularly toddlers, to have low red blood cell counts. See a doctor or hematologist if you are not doing so already.