Kettle Sizes

I am about to order my first all grain set up and am debating between kettle sizes. I'm considering going with 15/15/20 (MT/HLT/BK) or 20/20/30. I will be making 10-15 gallon batches for the most part to start, but also want to make smaller 5 gallon batches from time to time.

Is it possible to make 5 gallon batches in the larger kettles?

The thought process is to save money upfront by just buying the larger kettles if possible. Most likely going to go with a Megapot for the HLT and Boilermakers for the MT and BK.

you can definately make 5 gallon batches in larger kettles. i'd get the biggest thing you're willing to buy