Yeah it's a standard thing with sakura .. you can however edit this file:
gedit ~/.config/sakura/sakura.conf
and change ALL instances of
font=Ubuntu Mono,monospace 13
to whatever font/size you want,
Be aware there may be more than one instance of that line.
BTW, welcome to the forum

The other option would be to edit the sakura launchers (.desktop files) to start with say this command:-
sakura -f "Ubuntu Mono 16"
or whatever font/size you want.