Is Anyone able to tell me why my G-GM would have left at age 15 in 1866?

[Janelle]

And Renatha, I for one do count my blessings that my Catholic Irish 2nd great grandparents found the cash to leave Limerick, with their siblings, and first child, and so did come to Queensland July 1865.

They helped establish the village school and the RC church at Rosevale. 

Salute,

Janelle

[aghadowey]

You might find this paper regarding the population changes in co. Tyrone of interest-
http://www.billmacafee.com/sperrins/backgroundpapers/popntyrone1600-1991.pdf

[aghadowey]

As Sinann said a few posts earlier, immigration was normal. My great-grandmother and most of her 10 siblings (born 1850s & 1860s) left Ireland at some point. The family were very well educated and I found a record of their father travelling to Boston on business in the late 1840s shortly before his marriage in Ireland. Of this family-
1 son to U.S. then back with an American wife and children
1 son to Canada with wife and children
1 son to New York then Philadelphia
1 son to Australia then N.Z.
1 son stayed at home to farm
The daughters were no less adventurous-
2 daughters to U.S. (Baltimore, New York, Philadelphia) then back to Ireland
1 daughter to U.S. then back to Ireland, to Damascus then back to Ireland, to India then back home
2 daughters stayed home and married local farmers

Their mother came from a family of 14 (through their father's 2 marriages) and the children went to Australia, British Columbia and America.

[Renatha]

Thank you everyone for your comments, suggestions and attachments. I have found them to be of great help in getting a better picture of my G-GM's life in Ireland. She married my G-GF at 20yo (he was 29 & German) and they went on to have 8 children - 1 son and 7 daughters! My aunt gave me a framed portrait of Margaret & Ferdinand nearly 30 years ago, so for some reason I've always felt close to her. This recent search prompted me to finally take a photo of the portrait...She was nothing if not adventurous arriving in Melbourne in 1866 at 15yo then by 1870, getting married in Brisbane at 20. That's a long way! Aghadowey you seem to have found quite a lot of facts and figures about your Irish relatives and their travels! That publication was helpful.
Janelle when I think of the different parts of the world my g-parents and g-grandparents came from independently of each other yet coincidentally culminating at Brisbane, it has made me thankful I am even here on this planet! Sharonkai that link was great, thanks so much! Siann, since I started this thread recently there was a TV show about several UK rebels - English, Irish & Welsh transported to Australia in the 1800's and the Irish one - he was of the upper classes but fought for the rights of the poor - and there was a bit about the conditions at the time of the famine. Of course I've read fictional books set in that time, but I always thought my G-GM came after that and wondered why. But I'm realising from the large numbers, what an emigration took place over decades around that time.