Which one is it better between 15T and 25B for civilian job in the future?

Don't put either on a resume. De-militarize the job description and related it to the job you desire. Charlie Civilian wants to know what you can do in a language he [or she] understands. Sanitize the resume to delete to military jargon. Telling the potential employer that you were in the military is fine; however, speak and write in civilian terms during the job interview.

25B in my opinion. IT is a growing industry and there is alway a need for IT personnel in almost every job.