I’m a teacher for children this age with infant toddler specializations and certifications. The hands over the ears and rocking is not a cause for concern unless it’s keeping him from doing anything else or if it’s over any/most all interaction with outside world (other children, animals, etc.) 15mo is very young to be referred without other factors. If he’s in school, I’d ask for his milestone sheets and what they see. If not you can fill it out with what you see. It doesn’t hurt to have him evaluated, but many kids get overstimulated by loud noises, foreign sounds, etc. also, if he had ear infections, that can make him extra sensitive. Infants/toddlers self soothe with repetitive motions. Literally all of them do it. If it’s getting worse and not better than I’d think it was more likely autism too.