This is a very complex question. Essentially what Adobe is saying is you should have 10Gbit ie 10Gb Ethernet or Fiber connection per client to the shared storage. However SANs often are limited to the number of ports available on the SAN for connecting clients directly. For Example many SANs will have 2 to 4 base 10Gb ports either Fiber or Ethernet and have expansion options for another add on card or 2 that will allow 2 to 4 more ports per card. Since there are 10Gb Fiber cards with 4 ports that is the most common. The 10Gb Ethernet cards have been limited to 2 ports on most cards available. Many SANs that have 4 Fiber ports will also have a 2 port card for 10Gb Ethernet. What all of this means is even in ideal circumstances this allows only 12 ports for direct connection on average. You are referencing 15 client edit stations. So the requirement in this scenario would also require a 10Gb switch with fiber or Ethernet ports. SAN companies don't normally recommend adding a switch since it add's latency and the switch has a specific total throughput for all channels that must be divided by all clients. However it does work and the additional latency in 10Gb networks is marginal for the most port. It would show as maybe half a second more before the realtime playback starts.
On top of this allot of the networking handled by the storage along with the storage requests themselves is offloaded to the CPU for processing. The more clients accessing the storage at the same time, the greater the offload is. This means 15 clients connected to a SAN unit takes considerable resources. The SAN units are normally more limited in hardware specs compared to a Dual Xeon Server which has completely open hardware specs. This is due to the form factor and all in one solution SAN storage units provide. File Servers offer options for SAS storage expansions at much lower costs especially since you can chain SAS storage off the same raid controller several SAS storage units deep when they have the expander as most of the larger ones do. You can also add more than 1 network card whether 4 port fiber adapter or 2 port 10Gbe adapter and load balance across atleast 2 adapters to increase the bandwidth available for all clients accessing. The main reason SAN units are utilized is the latency factor of direct connecting editing clients to the storage host which is lower that way both for hardware communication and software protocols used. This gives the best performance for direct attached clients over a network. Either model SAN or Server works. But the amount of directly attached editing stations and storage requirements have a big impact on which is best for each production. I normally push most to the Server since it offers the greatest expandability at the best price and performance is solid. If you want to contact me directly we can discuss this but that is an overview of what Adobe is mentioning but can't really get into great details because there are so many variables here. Most SAN solutions do have proprietary software or license software from companies such as Editshare or Studio Network Solutions. These software licenses can be and often are expensive. The Server model doesn't require that software though but you can use it.