Which version of MacOS X and Photos are you using= The signature "iMac, OS X El Capitan (10.11.4)" cannot be right, if the "Image > Edit with" menu is available.
If adding text with Preview is causing problems, it may be a problem of incompatible or duplicate fonts.
You may want to check the fonts you have installed with the Fontbook application. Open Fontbook, select all fonts, and use the command "File > Validate Fonts". If there are problematic fonts, uninstall them withe the "Resolve ... " button, that will be shown, when a problem is detected by Fontbook.
To add text to a photo in Photos consider to use the Markup extension instead of "Edit with Preview". It offers the same text tools as Preview, but is better at saving the results back to Photos. You can call Markup, when you open your photo in Edit mode in Photos and click the three dot in the Toolbar. You may have to add it first using the "More" button. See:
Use Markup to add comments or draw on a photo in Photos on Mac - Apple Support