Download it here:
http://community.bistudio.com/wiki/ArmA_Beta_Patch_1.15

Changelog is:

5257 - Fixed: Game did not run on ATI cards in fullscreenmode on Vista x64 with large memory.
5257 - Fixed: Crash at ArmA.exe:0x174b27 - caused by wrong internal weapon state.
5257 - Fixed: Crash at ArmA.exe:0x56536 - caused by wrong turret state in MP.
5257 - Fixed: MP: Player driving motorcycle could be ejected with no apparent reason, sometimes leading to death.
5257 - Fixed: MP: Sometimes falling of a parachute a few meters above the ground.
5257 - Fixed: Dedicated server: Bandwidth balancing was often wrong, showing problems esp. when new players were joining.
5257 - Fixed: Players connecting JIP with custom files do not cause server lagging.
5257 - Fixed: Players with custom files get no longer kicked when server does not run on default port.
5257 - Optimized: Reduced memory usage with large view distances.
5257 - Fixed: Scene loading when starting a mission might sometimes use excessive amounts of memory.
5257 - Optimized: Slightly reduced VRAM usage with large view distances.
5257 - New: "Absolute" mouse control bindings (no auto centering) are now possible.
5257 - Improved: Provided error message for some unexpected memory initialization failures.
5258 - Fixed: Command line parameter -maxmem=xxx was not working on LINUX dedicated server.
5258 - Fixed: Crash at offset 0xfb57.
5259 - Fixed: Voice over Side channel could be transmitted to wrong listeners after respawn.
5260 - Fixed: Dedicated server crashed when script made soldier fire with Binocular.
5260 - Fixed: Grass and foliage was not affected by helicopter down wash since 1.04 version.
5260 - Fixed: status of disableAI was reset during save
5261 - Fixed: The FOV was deflected after TrackIR +tZ input had been removed from Zoom in/out action.
5262 - Fixed: Fast forward is now disabled when using binocular.
5262 - New: Optional server.cfg entry timeStampFormat to specify time stamp for each line in *.rpt file. Possible values: "none", "short", "full".
5262 - Fixed: Manual camera left/right movement was not mapped to mouse.
5262 - Fixed: Some AI commands on dedicated server might be delayed when the server window had focus.
5263 - Improved: Texture mip management more reliable in low VRAM conditions.
5264 - Fixed: Incorrect simulation importance for some entities in MP (for players in vehicles)
5264 - Fixed: Only relative path is now supported in commands: loadFile, exec, execVM, execFSM, preprocessFile, preproce