What Dosage Of Dexidrine Need To Be Taken To Treat Chronic Exhaustion?

I suffer from chronic exhaustion. My physician has put mt on 15mg Dexidrine time release capsul. I am only getting a small benefit from this dose. My question is can this dose be increased to see if I could get better results and have more energy to at least maintain minimal function if not attain a function level that I used to have.