Microsoft's Surface Laptop 3 may come in a 15-inch model
That's on top of a possible AMD-based version.
To date, you've had to buy a Surface Book 2 if you've wanted a Microsoft-made laptop larger than 13.5-inches. Soon, though, you might not have to spend quite so much to get a large surface. The historically accurate WinFuture claims that Microsoft will unveil a 15-inch flavor of the next Surface Laptop (presumably the Surface Laptop 3) at its October 2nd event. Most details aren't available at this stage, but Microsoft reportedly intends to preserve the taller-than-usual 3:2 screen aspect ratio like it did for the larger Surface Book.
There may be more shakeups at the media gathering. The Verge expects an AMD-powered Surface Laptop 3 (the first AMD-based Surface of any kind) at the event, although it's not certain if the new chip option would be available in the 15-inch system, the 13.5-inch variant or both.
The October 2nd presentation could have a wide variety of devices on tap, including an updated Surface Pro, a Qualcomm Snapdragon-based system and a teaser for a dual-screen Surface. It wouldn't represent a radical departure for Microsoft (outside of the teaser), but it would diversify a lineup that's still quite small.