Nice to hear that you're working on a new JT title
, I really hope it plugs the gab in the 1805-15 timeframe. 
But I have to wonder why you want to switch back to 15 minutes
, as far as I know the early games were 15 minutes and you decided to switch to 10 minutes for some good reasons 
.May I quote from your Jena Auerstedt notes:
"Campaign Jena-Auerstedt uses a 10 minute day turns and 30 minute night turns. This
was something that had been discussed for some time on various discussion boards in
an attempt to allow the players to react to enemy movement. The defender is able to react
in a more historical timeframe as a result.
Initial reactions by the Playtesters to a 10 minute move were mixed. Some thought it
would slow the game down too much. However, all of the Playtesters agreed after several
games that they preferred the new turn length given that the game didnt have any way for
the non-phasing player's infantry to form square prior to a charge. It also allowed artillery
to limber up and move away from a potentially dangerous situation."
Besides that I think 10 minutes are favored, I know we had either here or on another board a discussion about the early titles and that many still would like to see the scenarios of these games reworked from 15 to 10 minute or at least get an additional version that uses 10 minutes.
Currently there is a bit talk about reworking the historical scenario of the Waterloo game and the aim there will likely be 10 minutes too(at least on the one I would like to rework).
I would understand doing 15 minutes in a scenario benefits from this but unless this is the case I would prefer 10 minutes.
