12300 = 3600
16300 = 4800

You wont get a quality render in single-digit hours using any kind of beautiful atmosphere with a resolution of 4800x3600px

300 dpi is more for coffe-table books and art magazines like. For a painting that hangs on the wall and meant to be seen from some distance 150 dpi is sufficient. 2400x1600 is a more manageable resolution. But if you want a larger painting, say 32x24 inches, we are back to 4800x3600px again.

What I advocate, is that even as a beginner you should acustomate yourself to work in the larger format. It is a completly different workflow and if you don't do it from start you never will get into it.