Minn. Stat. § 580.21: ACTION TO SET ASIDE SALE; LIMITATION.

No such sale shall be held invalid or set aside unless the action in which its validity is called in question be commenced, or the defense alleging its invalidity be interposed, within 15 years after the date of such sale; provided that persons under disability, as provided in section 580.20, may commence such action or interpose such defense within the time therein provided. This section shall not affect or prejudice the rights of any bona fide purchaser.