1.4.8 is the current stable version.
1.5.4 is the latest release of the development branch.
so, yes, 1.5 is a thing.
people starting with scribus should get the stable version.
if you need features that are only in the development version, you're welcome to try it out.
for most things it's ok to use it in production. (and because of the long cycle leading to the next stable 1.6, it might be the only way for you to achieve your goals with scribus...)
just be careful about two (main) things:
- files that have been saved with 1.5 cannot be opened with 1.4 anymore (so, do your tests with a copy of your documents... and there is no way back...)
- features that were already in 1.4 should work well in 1.5, too. if you're using new features, you should test if they work well for you, before using them in production.