I may be mistaken, but my understanding is that there are currently no plans to produce a separate version of Swordpoint for 15mm. As I indicated above, Swordpoint works perfectly well for 15mm figures as it is, using the existing basing system and other rules as written. After all, 4cm frontage bases and 6' x 4' tabletops have long been the norm in 15mm miniatures wargaming. As an added bonus, the rules naturally work exactly the same for either 15/18mm or 25/28mm games.
For my own 18mm Swordpoint battles, the only adjustment I make is to measure all movement and shooting distances in cm rather than inches. Even that single change is simply a matter of personal taste and 'feel,' rather than necessity.
"Experience is the teacher of all things."
~ Gaius Julius Caesar