Has Ireland ever been called "Little Britain"?

Perhaps the island of Micra Bretannia.

The Roman geographer Ptolemy called the larger island Megale Brettania (Great Britain), and the smaller island of Ireland Micra Bretannia (Little Britain). Hence, originally, the term Great Britain referred to the largest island in the British Isles, similar to the Canary Islands where the third largest island is called Gran Canaria (probably thought to be the largest in Roman times), and the largest of the Comoros is Grande Comore..

More here

http://epicroadtrips.us/2003/summer/nola/nola_offsite/FQ_en.wikipedia.org/en.wikipedia.org/wiki/Britain.html#Etymology

Right, but strangely enough Brittanny, which is not part of the British Isles, also was given the name of Little Britain at a certain moment in history. https://en.wikipedia.org/wiki/Brittany

Interestingly enough...Little Britain is a literal translation of An Bhreatain Bheag, the Irish language name for Wales.

https://en.wikipedia.org/wiki/Little_Britain_(disambiguation)