I had to stop by and recommend Brink of Battle ( you can get it on Lulu.com ).
It fits what you requested, 5-15 models with almost roleplaying style characterization of each individual model. Although no vehicles... so 95% there ?
You can customize each guy dramatically... We create individual cards for each model, with name and all the individual stats for each guy...
It plays as a very tactical game, almost like a chess game. Last time we played we maneuvered for at least 4 turns before any shots were fired because we were trying to get each model into a good tactical position, based on their individual skills, before the firefight. This is possible due to an effective set of rules for sneak actions.
I started playing brink of battle because the CC mechanics were really original and unique for ancients/dark ages, but then we tried it for black poweder and finally for XXth centriury ( WWII and falklands ) and I was impressed. I had looked for a set like this before, I liked point blank and operation squad, but this one took it the extra mile by how much you can customize the individual models. Each period truly feels different although grounded on common operational mechanics, so the multiperiod portability is not achieved through abstraction or generic mechanics.
Have a look at a recent battle report and see if you think it might fit what you've been looking for http://leadadventureforum.com/index.php?topic=87059.0
The rules are pretty chromy, and it takes a some time to incorporate all the mechanics, so I created some QRS that go beyond the one in the book to make it easier for my group https://www.dropbox.com/sh/m2bsljdzl70nyss/AABTzHCB8yqnRUShY-8Td3Spa/QRS%20v2.pdf?dl=0
If the learning curve appears to steep for what you are hoping for then I give a +1 to operation squad, the models will be more generic than BoB but it is still a fun system.

You can find more about the game here https://www.facebook.com/groups/276411602433983/ and here http://www.brinkofbattle.com/
cheers..
Francisco