Can i bring my 15 years sister with my mother??

I will assume for purposes of your question that you are a US citizen in applying for your mother. Your sister unfortunately falls within another category than your mother, and probably the best thing is for your mother to immigrate, and then she can immediately sponsor your sister. Given the favorable quota situation presently, there is the possibility that your sister may be able to immigrate in the year after your mother enters the US. Due to the limitations of the Lawyers.com Forums, Alan Lee, Esq.'s (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided herein by the Firm is general, and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence.