If you are doing weddings, you really should consider a faster lens. That one might do you for outdoor stuff but inside the venue you will not be able to get a fast enough shutter speed.
Portraits, again you probably need better control over depth of field so the 15-85mm is not ideal.
Don't get me wrong, the 15-85mm is a corking lens, but it will do nothing you cannot currently achieve with the 18-135mm for the uses you mention.
Look at a 17-50mm or 24-70mm F2.8 zoom. With that budget I'd be looking at the Tamron 17-50mm F2.8 and a fast prime lens (50mm or 85mm F1.8)