Originally from a 68kMLA post at https://68kmla.org/forums/index.php?app=forums&module=forums&controller=topic&id=58945
I can't speak authoritatively on this, because I haven't looked at restore CDs from the era yet, but the AWGS machines were mostly marketed to particular potential with add-on software you could get, both from Apple and from third parties, and less to (as in the later years in the G3/G4/OSX-Server era when Apple definitely bundled AppleShare IP and later OS X Server) the built-in capabilities, of, for example, AppleShare/IP.
With that in mind the impression I've always gotten from 6150/8150/9150 materials is that the three were segmented based on intended use cases as well as workgroup/user base sizes. i.e. the 6150 might “prototypically” have served a single team of 20 or fewer people with a couple hundred megs of shared data and one or two printers, or run, alongside other machines or bigger ones, a single application or task (groupware like email/firstclass or a calendar application, or host a ClarisWorks database as part of a line of business apps.)
For example, see:
1997 AWGS article http://www.vectronicscollections.org/gallery/ads/macintosh/0275.php - talks about why you might need/want a server. 7250/7350/9650.
The 1997 brochure is really explicit about there being different software bundles for different ways you might have used a server, so you might, in 1997, have bought a 7250 to run a web site, another 7250 to run email, and a 9650 to stuff hard disks in to do local file service, and a 7350 to do a particular workflow task, for example.
Annoyingly, to the point of the original question, the 1994 68k/PPC AWGS brochure, which is the one that mentions the 6150, doesn't actually list specific server bundles, but Apple went hard on Mac servers running both their own and third party utilities for most of the '90s so it basically tracks that there was an appleshare 4 + powershare version, a version that was pretty much blank (just like a stock pmac6100/ would've been) and a version that, say, included some internet-focused software. (Especially since AppleShare IP 5 in like 1997 was the first version of AppleShare to bundle Internet-based services like web and email,
(what followed was some fan-fiction about a hypothetical many-disks Mac)