Re-read your post... I think you want to open associated drawing from part environment ? right ?
I am not sure if I had a custom add-in or if Open Drawing was available out of the box in 2015 but it is there as a valid option from what I can see in my 2015 installation. Open a part and then right click top browser node, do you have Open Drawing in the contextual menu?

This is how it will look in newer versions.

and here is an ilogi code for it ... Just in case I had a custom add-in and it's not available for you in 2015
Dim oDoc As Document
oDoc = ThisApplication.ActiveDocument
idwPathName = Left(oDoc.FullDocumentName, Len(oDoc.FullDocumentName) - 3) & "idw"
'check to see that the model has a drawing of the same path and name
If(System.IO.File.Exists(idwPathName)) Then
Dim oDrawDoc As DrawingDocument
oDrawDoc = ThisApplication.Documents.Open(idwPathName, True)
End If
Adrian S.
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AIP2012-2020 i7 6700k AMD R9 370
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