The 15th [and final?] patch was released before the first phase of the Beta ended. The Terran got multiple balance changes, the Zerg received one nerf, and the MMS that Battle.net uses for SC2 was improved. As always for undocumented Patch Changes, check out SC2Mapster.
StarCraft II Beta -- Patch 15 (version 0.17.0.15623)
The latest patch notes can always be found on the StarCraft II Beta General Discussion forum.
- Improved the system that handles initial placement and promotion/relegation between Leagues & Ladders.
- Weapon upgrade bonus decreased from 1 (+1 Light) to 1.
- Nitro Packs research cost decreased from 100/100 to 50/50.
- Siege Tank
- Siege Mode damage decreased from 60 to 50.
- Anti-air weapon upgrade bonus decreased from 1 (+1 Light) to 1.
- Brood Lord
- Weapon upgrade bonus decreased from 3 to 2.