In May I will be traveling 3.5 hrs and would like to bring my dog with me. He is about 15 lbs and is 1 yr old. Well mannered. Do I need to get him sleeping pills from the Vet?

First and foremost, consult the airline about the specific guidelines for flight-each one has different rules! You should be able to take him in a small, collapsable carrier in the plane with you. All flight require a health certificate 10 days or less before flight. This only comes from a vet. All also require current rabies vaccination and proof of rabies-use established vet where rabies shot was given and kill 2 birds with 1 stone because in filling out health cert. vet needs rabies vacc info.
OK!
You have to be careful with sedatives or tranquilizers and altitude. Consult vet and maybe "test drive" one before flying if he/she suggests it. If pet is normally calm, it may not be needed.

Check specifically with the airline on a collapsible carrier. Most of them require the solid plastic ones such as the Pet Porter or Vari-Kennel brands. Make sure it has no more than enough room to stretch out in. Many airlines apply the same size restrictions to dog crates as any other carry on luggage. If you can't keep him in the cabin, the FAA now requires airlines to keep records of pet deaths. A major factor on selecting an airline.

If he is at all excitable or doesn't accept new experiences well, yes talk to the vet. It will be even more important if he isn't used to being crated. You might also get the crate ahead of time and let him get used to it.

A dog that has not been crated since it was little, make take some work.
Start just putting its toys and treats in the crate. Praise it for going
in. If you have been able to trust it with any bedding, put that in the crate.
Feed it in the crate.