So that would rule out the Debian specific options (FWIW v15.x is based on Debian 9/Stretch).

So that leaves the "Other Linux-Kernel" options. As Debian 8/Jessie has a v3.16 kernel, one of the "Other Linux-Kernel 3.x or higher" as being your best option.

Whether to use the 32 or 64 bit option will depend on whether you have a 32 bit (i.e. 'i386') or 64 bit (i.e. 'amd64') build. FWIW v14.0 & v14.1 both had limited 32 bit release; v14.2+, including v15.x are only available in 64 bit.

If you are unsure, if you are launching from ISO (or one of our other builds), then you can check the filename. Alternatively, if you are migrating from a different platform, then please run 'turnkey-version' on the running server. Either way, you should have something like this:

turnkey-lamp-14.0-jessie-amd64
# or
turnkey-lamp-14.0-jessie-i386

From that you can work out which architecture you need to select. As hinted above, 32 bit will include 'i386' in the filename/'turnkey-version' output. Whereas 64 bit build will include 'amd64' instead.

Hope that helps.