Power Bi Desktop very slow

With a dataset of that size, the most likely problem is that your DAX measures are not written efficiently and could likely perform much faster if rewritten appropriately. It's not likely that better hardware would make nearly as much difference as optimizing the measures.

I've had similar experiences with similarly sized tables when the logic got highly complex (or was written without performance in mind). I ended up consulting with Marco Russo to help determine exactly where the bottlenecks were in the calculations and rewriting many of them from scratch for much-improved performance.

Without any knowledge of your particular data model, all I can suggest is to seek out optimization information. Microsoft has some advice and sqlbi.com has great content too.