In Minnesota, DUIs escalate based on the number of prior DUIs. So, your brother might be charged with a 3rd degree DUI, which is a gross misdemeanor. If he is convicted, he could face some jail time. I would recommend he speak to a criminal defense lawyer to figure out whether he has any defenses or whether a plea agreement could be reached.
Many lawyers, including myself, offer free consultations where they generally discuss the case with you. I recommend that he contacts a lawyer as soon as possible.
Mr. Rice is correct - It appears your brother will be charged with a Third Degree Gross Misdemeanor DWI. (This assumes that he has one alcohol-related conviction/revocation within the past 10 years, did not have a child in the car, was not involved in a car accident involving injuries, and provided a breath sample post-arrest which was .15.)
The maximum penalty for a gross misdemeanor offense is one year in jail and a $3000 fine. There is also a statutory minimum sentence for a repeat DWI offender. He will receive a revocation of his driving privileges and a notice require him to display serialized license plates (a.k.a. Whiskey plates).
There certainly may be viable legal issues in his case that can do him great good. If he submitted to a breath test at the station on an Intoxilyzer 5000 machine, the use of this test can be challenged. Your brother should schedule a consultion with an attorney to discuss his case and determine what legal issues may exist. Further, the revocation and imposition of the license plates must be challenged within 30 days of when he received notice, which is likely the date of the offense. It is important for him to hire a skilled DWI attorney immediately. He can contact my firm to schedule a consultation.
What will happen could depend upon whether he retains a DWI defense lawyer to help him. If he does, he might win the whole thing.
A second in 10 carries more serious consequences than a first, including a 30 day mandatory minimum jail term if convicted, and a longer drivers license revocation period if that is not challenged in court (within 30 days) and won.
The potential outcome depends upon which county the case is in and which testing method was used by the police. If your brother submitted to an Intoxilyzer 5000 test, he has a defense based upon a challenge to the machine's validity and reliability. In general, he should avail himself of a free consultation with a lawyer to learn what his options are.