You can switch to the Iray renderer in the 3D viewport, this will allow you to render at any resolution and will give you much better lighting and reflections.
Thank you for your answer. About photogrammetry: Agisoft, or are you using the Autodesk one that does the render for you on this cloud thing? (or another one?)
are you really saying that you made everything by yourself? if so, then damn, that's impressive. cause it looks like you put some serious work into this.