I have a 55 minute connection at BRU coming up. I've done a bunch of research and determined that my United Flight from ORD will be arriving at a B gate at 9:05am (if on time) and my Brussels Airlines flight to MRS will leaving from an A gate at 10am. Would it be quicker to take the bus transfer between B and A gates, or to walk between the gates? I'm assuming I go through passport control at BRU and not my final destination, MRS.

Thanks.