I humbly suggest that you research.
There are many actual commercial distilleries already using smaller barrels.
Such as the place I bought my once used Bourbon barrels, 15 gallon size.
Oola in Seattle is the place
They make a high quality Bourbon and they use 15 gallon barrels.
I used one to age my current batch of Panela rum, the 2017.
It is very good, if we were closer geographically I'd share.
I just suggest before committing to a 15 to 20 year aging process in a 55 gallon barrel that you check it out, I mean there's a lot that can happen in that amount of time.
See what real micro distilleries are using, in the case of Oola it's 15 gallon virgin white oak barrels for their Bourbon.
A 15 gallon barrel seemed the right size for what I wanted and how much time I wanted to commit to aging my rum.
Turns out that was a very good choice.
Of course - you do you.