Should I send my son to preschool to improve his speech?

My husband and I have a 2 1/2 year old toddler. Our son knows more signs than spoken words. In the last few months, he has picked up more words. But not as many sentences. The speech therapist recommends preschool to perhaps help pick up more sentences. Theres two great preschools. one is 2 days for three hours and the other one is 3 days and 4 hours. How do we know what is too much / too overwhelming for our kid? Any feedback or suggestions will be great. We have been hearing great feedback. Either school sounds great to us. They both have a low student/teacher ratio. Thanks for your help in advance.