The film works better without the additional scenes. Director Adrian Lynne made this decision (as he discusses in the commentary) and he was right. They're fascinating, but ultimately Jacob's Ladder perfect in every way.
I got duped by Amazon too. I thought I ordered the 18 cert, but it arrived this morning and its the bloody 15 version!! RIP OFF. Amazon, you should be bloody ashamed of yourselves. I did go on the BBFC website and it says the 15 version has not been cut and that the smaller film time for the DVD is due to the cinema FPS being 4% faster. I didn't know Adrian Lyne said he left the additional scenes out. But on Region 2 DVD the only "extra" is the trailer. No commentary or nothing. We get a really bad deal here in the UK when it comes to our DVDs :-(