On a second DUI conviction with a BAC of .15 may bring extra penalties, and it may not. It depends on the case itself, the court you are in, and the attorney you have negotiating your case. In the plea bargain phases, the prosecutor may insist on additional jail time in the offer (more than what the prosecutor would have been offering if your BAC was below a .15), extra AA's, and perhaps other programs such as MADD or VIP (which prosecutors in Los Angeles like to add when the defendant is on the young side). If you are not in one of the 4 pilot programs that makes an IID mandatory, the prosecutor may include an IID as part of the plea.
There really are a lot of variables. If your court case is in Northern California, you should hire an attorney around there, and call a few in the process to get their opinions about the matter since they will be more familiar with the Courts and prosecutors up there. There are potential serious consequences and defending yourself in the case is not advisable.
For the most part the BAC for a second DUI does not truly increase the penalties one would receive. The BAC is an important factor when dealing with a first DUI as it could mean the difference between a 3, 6, or 9 month class and in some counties it could be the difference between jail time and no jail time. I would make sure you contact a local DUI attorney in your area as there are differences in the courts and you will want to discuss this with an attorney that is familiar with the court you will be going to.
A second DUI carries a mandatory 96 hours in custody. The above .15 BAC allegation could result in additional jail time, public works, AA meetings or community service. The court will look to factors such as length between previous DUI, other criminal history, your personal situation, etc to determine what additional punishment is appropriate in your situation. Contact a few Sacramento DUI attorneys and discuss your case with them.
If it's a second DUI within 10 years in Sacramento County, the D.A.'s office will look at the BAC (.15 and higher is not good), the recency of the prior DUI (the closer in time, the worse off you may be situated) and how bad the actual driving was (e.g. was there an accident) and perfomance on FSTs. As convicted second offenders typically have to take an 18-month DUI class, the enhancement will most likely apply to the length of a sentence, with 10 days being the minimum. On a standard early resolution, the DA typically seeks additional days of jail (or alternative) based on the BAC.
I would recommend that you consult with a few local attorneys, to whom you can provide additional facts so that you can get a clearer picture of what lies ahead, and make a reasoned determination about whether you should hire an attorney to assist you with your case.
Probation in Sacramento County on a misdemeanor DUI with a prior conviction is for a period of four years, and you would be at risk for severe consequences if you are arrested again for a DUI.