If you receive a sentence of between 12 and 15 months, you will be sent to a minimum security and possibly short term institution.
No one can predict what a Judge may do. The Judge does not have to follow the guidelines. I suggest you discuss with your lawyer whether you have a good argument to get the Judge to depart downward.
The above answer, and any follow up comments or emails is for informational purposes only and not meant as legal advice.
YES, you can. IF the statute you were convicted of prohibits probation, then you cannot get probation for that reason, however. Because the guidelines are now not mandatory, the court may sentence anyone to probation regardless of zone, unless prohibited by the statute of conviction. Your lawyer should know this. You need a federal Attorny who really knows the law. You will not get probation, even if the statute of conviction bars it, unless your Attorny knows what she is doing and actively works to convince the judge to give it to you.
If you are in Zone C the only way you can get probation only is for the Court to grant a variance which would cause you to move to Zone A. Zone A is the only United States Sentencing Guideline category in which a person can get only probation.
You are confusing the guideline calculation which provides an advisory range of sentencing to the sentencing judge with the discretion of the judge in the specific case.
This answer/response is based on the information provided in the question asked and requires a much more complete context than is available in this public forum. Please do NOT use this answer/response to say or do anything regarding your situation. BEFORE you say or do anything consult with an experienced Federal and/or state criminal defense attorney in your jurisdiction who will listen to you and your concerns.