I have tested Photoshop CS5, and it still works with El Capitan, Mac OS X 10.11.4; however, it requires one additional software installation.
Now that I remember, this was required in Yosemite as well. Installing an additional version of Java is needed for this “vintage” software to operate.
Java for OS X 2015-001 can be downloaded from https://support.apple.com/kb/DL1572?locale=en_US
On my system, I simply opened the .dmg file and launched the installer. I did not even have to restart my computer. CS5 started immediately.
Let me know if you have any problems.