Eureka, Old Glory and Blue Moon are all outstandings (multiposes, nice sculpts), but are all 18mm. As is Essex (nice sculpts too but monopose).
For true 15mm, try Minifigs or Freikorps (all monopose). For multipose, you could try Peter Pig American Revolution Range infantry with bicorns and old cut uniforms, and paint them white ignoring the non-French looking equipment.
There are so few uniforms variations in the SYW (anyway, so few that would be noticeable in 15mm), that most ranges are complete or are not difficult to complete with proxies (e.g: you could easily model all kind of hussards with a single sculpt).
Moreover, the distinctly "French cut" for the infantry (closed vest, without turnback, and with a belt on top of it) rapidly evolved during the war, and by 1760 the fashion was to have the vest open, with turnbacks, and the belt under - an appearance very similar to the other nations: Brits, Austrians or Prussians (both with tricorn pompoms cut off), can all make good proxies to French (the lapels can be easily hidden by the paintjob - and remember that some French regiments, like Auvergne, had lapels anyway).