If I am still on probation and was arrested with 15 grams of Meth, will I go to prison? Do I need to get an attorney?

Yes, you definitely need to get an attorney for the current meth charge and for the probation revocation hearing for the previous charge that you are on probation for. The arrest for me this a violation of your probation, so there will be a probation revocation hearing for that charge. The judge could revoke your probation and sentence you for the original offense.