Some babies don't speak much until they can speak in whole sentences.

Try to do things that relax people with SPD. If he seems more engaged and happy (even if he isn't speaking) then you will know SPD is the problem and just need to make some minor life adjustments for that.

SPD if treated early and the child knows how to self maintain will mostly just be an annoyance at times for them, but they will be otherwise normal. If SPD isn't treated or maintained sensitivity levels can keep growing pushing past the annoyance level into an actual disability level. Anger management problems, crying for no known reason, and/or incapability of doing anything are examples of negative side effects of disability level SPD. They sometimes get diagnosed as other problems, but the cause is their brain overreacting to outside stimulous.