St Leonard is the patron Saint of prisoners, and only a couple of Suffolk churches are dedicated to him. Despite the entirely 19th century windows, the church is clearly of Norman origins and the walls slope significantly towards each other as they approach the east. Perhaps there was once an apse. The bell-turret is a tribute to the proximity of Essex, and inside the south porch the doorway confirms your theory about the Normans.
The Victorians undertook a major restoration and the overwhelming feeling inside is of 1880s gloom. This isn't as dull as it sounds, for the church is neat and well-kept, and provides a document of, and testimony to, parish life over the last couple of centuries. The only medieval survival is the font, but there are a couple of nice 18th century memorials, including one with a splendid skull.
(With thanks to Simon Knott - http://www.suffolkchurches.co.uk/wixoe.htm)