Hi,
I have maybe the same problem.
I upgraded two websites from 1.5.14 to 1.5.15 (i stop here at this moment and try to fix the problem).
When SEF System Plugin is activated, i have the classical error "Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 6948121 bytes) in /home/www/www.billet-invest.fr/web/plugins/system/sef.php on line 69". And the problem is not the memory.
Of course, none problem before upgrade. I unpublish sef plugin, of course no more error but in this case a problem for all images. The website is with this last configuration. And no way to activate again SEF plugin whitout the error.
http://www.billet-invest.fr/Many thanks for your help.
Best Regards.