Consider:
Where do I go and how do I increase the FontSize in this drop down menu to make it more easy to read?
Consider:
Where do I go and how do I increase the FontSize in this drop down menu to make it more easy to read?
Details of the solution and additional comments may be found in: How to change the default font for all cells in all notebooks
Format / Edit StylesheetCore.nb (no all of them, only selected on a picture below)(the Core.nb is in $InstallationDirectory/SystemFiles/FrontEnd/Stylesheets)
"CodeAssistCompletion" and "CodeAssistUsage", the rest will inherit it.