I use the main answer of this question quite often to clear some space, but now I'm in extreme need and I'd like to better understand which kernels are safe to purge, my list is the following

10:50:58-673 - ~> dpkg -l | grep -Eo "^.i +linux-(image|headers)[^ ]+" | cut -c 5- | grep --color -E "$|"`uname -r`
linux-headers-2.6.38-15
linux-headers-2.6.38-15-generic
linux-headers-2.6.38-15-generic-pae
linux-headers-2.6.38-16
linux-headers-2.6.38-16-generic
linux-headers-2.6.38-16-generic-pae # current one
linux-headers-generic
linux-headers-generic-pae
linux-headers-server
linux-image-2.6.38-15-generic-pae
linux-image-2.6.38-16-generic-pae
linux-image-generic-pae
linux-image-server

Is it enough to keep

linux-headers-2.6.38-15
linux-headers-2.6.38-15-generic
linux-headers-2.6.38-15-generic-pae
linux-headers-2.6.38-16
linux-headers-2.6.38-16-generic
linux-headers-2.6.38-16-generic-pae # current one

Or would this be enough

linux-headers-2.6.38-15-generic-pae
linux-headers-2.6.38-16-generic-pae # current one

Or which other would be the shortest (keeping the previous one too)? And why?