I have a late 2013 15" rMBP (i7/2.3/16GB/1TB) which generally still runs very well. I use Parallels 12 to run excel in windows (I work in financial reporting). I usually have a bunch of excel windows open through parallels and the laptop struggles a lot with that. The fans start going and the windows get a bit laggy and I sometimes start seeing artifacts and graphics anomalies. Is this due to limitations of my cyrrent CPU? RAM? or Graphics Card? I'm planning on getting a new 15" 2018 MBP (2.6/16/512) and I'm wondering if getting 32GB RAM instead of 16GB would help with this or whether 16GB is enough already and whether I can expect the new machine to perform better.