There's several ways to go about it. I listed my research experiences and my publication from those jobs as two different things. My justification is that I did many things while on the job - patient interaction, testing patients, solving problems with equipment, etc. The publication is a detailed description of one experiment and what the results meant. These are two very different things you are describing, and I believe it can be confusing to an ADCOM to list them together.
If you have many publications about different facets of the same general research question, I'd lump them together and list their references (so the ADCOM can look them up) and tell the general results (these papers showed that XYZ is good for ABC populations because of 123 reasons). As always, use all of the space you can on your AMCAS. For example, I have biomaterials and biomechanics experience, so I listed these as two different experiences. I listed the strings of publications that resulted from these different projects separately.
In with these guiding ideas, I've thought that while you want to use all 15 EC spots, (assuming you have good stuff to use them on,) you want to use them on a range of items. For example, you did a year-long research job that resulted in 2 presentations, an abstract, and a full-length journal article. You could list them:
1 research experience (lumping everything together)
Or:
1 research experience
1 publication (lump all pubs together)
Or:
1 paid job experience (if you've already got a research experience listed)
1 poster
1 presentation (lump presentations together)
1 publication (lump abstract and journal article together)
I would choose to use this last method. It shows a much greater breadth of experience (uses 4 different categories of ECs) as well as giving you space to write about each separate one. The grouped ones are probably closely related, so you can double-up without sacrificing content. You also condense things enough that you don't look like you're stretching things. Given that most schools probably can only assign some points to each catergory of EC (e.g. 0-5 points), having 5 good experiences in 5 different ECs is better (4 x 5 = 20 total EC score) than 5 great experiences in 1 single category (5 x 1 = 5 total EC score).
