Chair leather is too glossy and seems to lack the surface pitting/pattern that leather exhibits. Should probably be a touch darker too, and turn on a touch of SSS if you haven't, leather is dried skin, it absorbs and blends light a bit. Even the synthetic stuff behaves somewhat similar.
Edges on your windowsill looks way too sharp.
Light on the windowsill is overblown and the low resolution of your HDRi background creates a bit of an eye-sore.