Basically, you can't.
J1.5 templates WILL NOT work on J1.6 installs.
Half a dozen or so templates have been converted at this point with others on the way...
You don't mention which template you are using, but in any case, they are being converted from newest to oldest, same as the J1.0 to J1.5 templates were.
Rob Snow wrote:
As my subscription has ran out, how can I get the template to work in 1.6?
To get a copy of the J1.6 template, when it arrives, you will need a current subscription to download it.