It is generally not recommended to have more than 500 fonts installed at any one time.
One of the reasons being the problem you are having.
When Photoshop starts up it reads all the fonts in the font folder.
The more you got the longer it takes.
Accessing this many fonts also uses up more system resources.
You may have them but how many do you actually use?
I have 15.000 plus fonts. All on the drive but less than 500 in the font folder and probably less than half of those I rarely if ever use.
All my extra fonts are in a separate folder sorted into categories or types of fonts.
I use a font program called "The Font Thing" for keeping track of them.
If I want to create a flyer and need a font for a header I find it, install it, print the flyer and then uninstall it. If I need to do an update on the flyer in the near future I leave it.
You need to clear the Windows font folder of all the extra fonts you don't use.
First create a new folder for them. Sub folders can be created later if you want to sort into categories.
COPY and paste the font files from the windows font folder to the new one. DO NOT cut and paste. There are fonts in the folder known as system fonts which the O/S uses by default. For example the header font on the active title bar at the top of your screen.
DO NOT uninstall or delete any font which has an "A" or an "O" on it's icon. These are system fonts. Examples are arial, courier, comic sans and Times New Roman.
Icons with a "TT" can be uninstalled.
Fonts are best uninstalled using The Font Thing.
Each time you click on the font name the font is displayed on the viewer pane. Quickest way to check if you need it or not.
http://www.softpedia.com/get/Others/Font-Utils/The-Font-Thing.shtml
I've got all mine burned to disk as well as on external drive.
I like to play safe.