Yes. As Kryo said:
DA uses some files from GC2.
There's no standalone update to 1.5 at this time. I don't know when or even if we will be posting a standalone update for 1.5, but chances are you'll have to wait until the dust from Dark Avatar settles a bit.
If you want the 1.5 update now, you will have to use Stardock Central to get it.
There are many great features available to you once you register, including:
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