While there are a couple of methods in PowerPoint for reusing slide content, I don't think any of them quite work as you'd prefer. Of course, you can select Insert > New Slide > Reuse Slides, but this copies the selected slides into your presentation.
You could select Insert > Object, choose Create from file, and then check Link. This will insert the presentation as a linked object, but this comes with some pretty severe limitations. First, it's not slide-specific, so you're basically getting the entire presentation. Also, while you're editing, PowerPoint treats the linked content like a picture; that is, you need to place it on a slide and resize it, etc. When you run the host show and get to the slide containing the linked content, you have to click the content to activate it. The linked presentation then opens and runs. Once complete, it returns to the host presentation (still in progress) and continues. Honestly, it's pretty janky, and more often than not, it ends up crashing PowerPoint. So, I wouldn't recommend it.
You could also create a shape (could even be a thumbnail of the target slide) somewhere on a slide in your host presentation and then select Insert > Action, choose Hyperlink to, and then choose Other PowerPoint Presentation. This has the added bonus of allowing you to choose which slide you start in the linked presentation. But it still takes a noticeable amount of time to load the linked presentation. Plus, you may get a lot of pop ups and (depending on your trust settings) some security warnings, too. And because it's external to the host presentation, it doesn't exactly appear in your host presentation's flow, which means you might accidentally sail right past it if you forget to actually click the anchor. So, YMMV.
Regardless, all of these are basically hacks, as PowerPoint doesn't really offer a feature to seamlessly link to slides from other presentations.
You might want to look at a third-party content management tool that can handle this for you, such as Flare. However, that adds an extraordinary amount of overhead for something a relatively simple as reusing slide content.
