15"?
The 12.3" 2736 x 1824 Surface Pro 7 with Core i5 and lower is fanless, and AFAIK some 13" 3000 x 2000 Surface Books without dGPU are fanless too (at least SB2, don't know about SB3). The ones with a dGPU in the keyboard only start the fans when you use it for rendering or compute.
I don't know any 15" fanless laptop with a 4K screen. It's a weird set of requirements, at least to me.