I have a 21m age gap, so not that dissimilar from what you will have.
OK, good things about two boys - here goes:
A brother is an amazing thing for a boy to have - who else can they play engines with, who else will really understand the importance of the difference between the narrow gauge Skarloey and Duncan, ordinary steamies Thomas, James and Edward and the somewhat evil diesels Iron 'Arry and Iron Bert?
You can use all the same clothes again - and your second son will suit all the stuff you didn't quite like on your oldest (weird, but it's happened to me!).
They have a natural choice best man in the future and they won't upset any friends with their choice.
They can share toxic aftershave when they're teenagers.
You can say "the boys" without having to always say "the children" or calling them "the kids" if you don't like that shortening (which I don't, but I'm a ponce).
Oh, and loads more. I don't feel I've missed anything by not having a DD - I think I'd have been more anxious about projecting my "I'm an insecure woman with self-loathing tendencies" onto her.