You can safely increase memory limit to much higher value.
The price of a block of RAM is very small. Increase php memory limit to 512Mb and see how it goes. That might the simplest solution to try:-)
Funny thing is my machines do not exhibit lack of memory. I run <System Monitor> most of the time and do "top" checks in a terminal frequently. I mentioned in a previous email that I had tested this on my machine and went as far as 2048M but after 512M the problem worsened by degrees, so throwing more memory isn't the solution. Roger