Joomla 1.5.7 to 1.5.23

I have searched all over for a solution but cant seem to find the answer im looking for.

I am using the iLife template, which I understand is an old template, but I would like to know if it is 'safe' to upgrade my version of Joomla to the latest version and if it will still be compatible?

I have developed most of the website already and dont want to have to start all over again should there be a compatibalilty issue.

I have tried using certain modules which I am finding are not vampatible with such an old version of Joomla. I am also concerned about security risks with these older versions (1.5.7) supplied with the quickstart template.

Is it possible to upgrade my version of Joomla (1.5.7) to a newer version based on this template...and if so, what version is best?