A planted buffer area of not less than 25 feet in width shall be maintained wherever new units abut zone boundaries except when coterminous with existing roads. When land abuts existing R-150 development of two or more lots, the land immediately adjacent to the existing R-150 development shall be developed in accordance with all R-150 Zone requirements. In addition, a seventy-five-foot wide minimum setback, including the twenty five-foot planted buffer, shall be maintained between the new R-150 units and any new units of greater density, said buffer to be in addition to any existing or proposed streets.