The total manpower/IC is the same, if we use 6 x10 div instead of 4x15w, then there is a chance that the defense stat per each div is too small and get crit damage.
If we're ignoring supports and we're inventing a half width infantry battalion to keep total manpower/IC the same, org for either template would be the same, so having more templates means more org.
If we assume a theoretical 100 defense for the 10w, and increase it by 50% for the 15w to 150, there is a specific window between 121 and 187 attacks (or 121% to 187% of the value used for the defenses of the 10w) that the 15w has more e-org than the 10w, in all other cases they have less e-org. You can scale the numbers up or down to fit whatever specific values you are getting in game, just remember to keep the ratios the same. If you wanted to change the ratios of defenses between these 10w and 15w, I'd have to come up with a new graph. Whenever one of the 10w suffer any more than 100% of their defense value they will be suffering whatever amount of increase HP damage, regardless of their total e-org though.
Now the question shifts to how likely each of those formations are to be sitting within that window, but that depends on a lot of factors. How many enemy formations there are, how big they are, how many attacks they have, what their coordination is, etc. I'm going to assume there are only 2 enemy formations and they are at least 30w with 35% coordination, such that in our 4x15 or 6x10 scenario, all of them are being targeted and the math is way simpler for me to use.
We can see that unlike before where there was a specific window where you'd be taking increased org damage, we can see that accounting for the spread of attacks based on coordination and such, there is a specific window where the smaller template even suffers more damage than the larger template. Now, these windows are particularly large, for 35% it ranges from 219 up to 923, for 50% it is 172 to 1199, and for 66.2% it is 140 to 1775. Now, if we add the E-org line that we saw in the earlier damage graph, we can see something really interesting.
There is a very small window from 182 to 220, and only with very high levels of coordination, where the total e-org of the larger template is higher than the smaller template, and only by a comparatively small amount.
Of course, the information these graphs give us only applies to specific scenarios, but it is still interesting.