My office is located at 69 Newbury St. We are in the 2nd block, located in 02116. This zipcode covers the heart of the Back Bay, and all the way over into the South End, right at Calderwood Pavillion. (Many people find this surprising). The 02115 zipcode hovers at Mass Ave and across Mass Ave. The value in the 02116, in my humble opinion, is a better value, on many levels.
Stop by my office and I can show you maps and help who you understand the differences.