8GB of VRAM is the minimum recommended for the remove tool.
If you have less, the operation will likely be processed on the CPU and thus be VERY slow. Also, larger remove areas might not fit into VRAM so you’ll likely be better off using several small masks (especially if working on high resolution images).
And yes, here Topaz is more demanding than other softwares as it is doing the process locally on your PC and not remotely / “in the cloud” as e.g. Adobes solution.
