I am not positive this is a stylized painting after 18th century work or painting of French King Louis XV, but it seems most likely. Given the time to search early to mid-1700s European rulers, it could possibly be another Royal. A little souvenir, it seems to me it might have been mounted into the top of a box, a snuff or powder jar, perhaps. The outer frame you see in 2" in diameter and is silver.
Very good to excellent condition for age and type - as noted, seems to me to be a portrait which is salvaged or removed from a small box like a snuff or patch box. See photos of back. The silver frame, the convex cover glass and the little painting are each perfectly preserved as you see them. Great for a collection of Royals, or of Grand Tour souvenirs which I believe it most likely is. Full measurements noted on photos.