Mentioning future work, that is now complete
The material is highly relevant to your presentation so you don't need to ask people on the internet whether it should be included.

You can and should mention it. Your talk should be based on the current best understanding of the subject, whether that comes from your conference paper or from a subsequent journal submission. It would be silly to give a talk about how, for example, your experiments show that gravity causes apples fall from trees and you're planning future experiments about its effect on other fruit, if you'd already done those experiments and, in fact, submitted a journal paper about how gravity causes all massive objects to be attracted to one another. Indeed, I've often been to conference talks where people have presented stronger results than they'd originally submitted. That's just a natural consequence of the submission deadline being some time in advance of the conference.

In a comment, you mentioned that you were worried because the originally submitted material has been peer-reviewed but the more recent material hasn't. That's a legitimate concern but not, I think, a serious one. Conference reviewing is very much "PeerReview lite&trade;" and reviews are more at the level of "There's nothing obviously wrong with this and I think it's interesting enough to be in the conference." Journal reviewing aims more towards "As far as I can see, this is correct."  Since your original submission was of an appropriate standard, it's very likely that the additional material is of a similar and acceptable standard. Given that you were confident enough to submit that material to a journal, you should be confident enough in its correctness to tell people at the conference about it.