Is it possible to attain stream-entry if one is only following "the 5 precepts"? Is it possible to attain stream-entry if one is only following "the 5 precepts"?

Are there any suttas that seem to address this question?
"entering the stream" means you understood the main point of Buddhism and started applying that point to your entire life.

Which point? -- That you should stop creating causes for future dukkha.

Which causes create dukkha? -- Whatever leads to increase of conflict, increase of side-taking, increase of attachment, increase of obsession, increase of aversion, increase of ignorance - leads to increase of dukkha. Whatever leads to maintenance of conflict, maintenance of side-taking, maintenance of attachment, maintenance of obsession, maintenance of aversion, maintenance of ignorance - leads to maintenance of dukkha. Whatever leads to cessation of conflict, cessation of side-taking, cessation of attachment, cessation of obsession, cessation of aversion, cessation of ignorance - leads to cessation of dukkha. 

The nature of dukkha is conflict, clash, mismatch - so if you are setting in motion forces that will set up conditions for arising of conflict, clash, mismatch - then that's what you will get. Once you get that - there's suffering. Correspondingly, when you are laying down causes in the here and now that are by nature conducive to harmony - then that's what you'll get. It is that simple. We create Dukkha by ourselves, so once we stop creating Dukkha we may still get some Dukkha created in the past, but eventually all the past causes will run out and the new causes will come to effect, and so gradually we will attain the natural harmonious state - Nirvana.

Once you really "get" this, once you see it clearly, then you stop acting like that, because you know it's for your own benefit. It's not just blindly following the five precepts. It's about getting the principle. Sometimes you may still make mistakes and create trouble - but as long as you got the principle in the overall - you will keep making progress.

This is when we say you are "in the stream" leading to Nirvana.