As I've pointed out in the past, these games at Wrigley Field with unusually high lines go OVER more times than not. It has very little to do with the pitchers but more-so with the extremely significant winds blowing out, which is the only occasion when Vegas busts out the rare high lines. Even if Matt Cain was pitching, the line would still be in double-digits, although not nearly as drastic. Off the top of my head, there was a Wandy Rodriguez start either last year or the year before with a line of 13+. Chris Young in his prime two years ago garnered a similar line 2-3 years ago.
This is not a situation to bet on UNLESS you have a strong under vibe that one or both pitchers will excel today, or if you simply believe both pitchers will get bombed (Which will be tough with someone solid like Leake and a guy on the rise like Rusin coming off a good start).
Nobody studies baseball over/unders more than I do and I can assure you this not a trend you bet on just "because it fits the mold." You take it on a case-by-case basis, and even then it's tough with those winds. Plus, on occasion, the winds change throughout the game, which CANNOT be predicted at all.
Best bet for these games is to just show some discipline, lay off, and not bet.