BOSTON — KS Partners LLC has acquired 15 Court Square, an 11-story office building with ground-floor retail space in downtown Boston. The sales price was undisclosed. The 82,000-square-foot property, which is also known as 15 Pi Alley, includes an on-site tailor, 24-hour maintenance and an ATM. At the time of sale, 15 Court Square was 98 percent leased. KS Partners acquired the building from Brickpoint Properties, which had owned the property since 1978. KS Partners plans to fully renovate the lobby and common areas of the property and add amenities such as a lounge, conference room, fitness center and bike room.