from this bug report
https://bugs.scribus.net/view.php?id=12788it seems that calibri cannot be embedded with 1.4.
if it cannot be embedded because it's an otf font, then there are good chances that 1.5 will be able to embed it.
if you should use the dev version of scribus or not depends on a few parameters.
if you're otherwise happy with 1.4, stick to it and try to get a different font (if it's possible for you)
if you want moar! then you might want to try 1.5.
just be warned that files saved with 1.5 cannot be opened with 1.4 anymore... so only try it on copies of your real documents!
each time i have to open 1.4, i have the feeling that scribus 1.5 is a completely new program... : - )