Delete Text on title slide

For your second suggestion, I don't get a title slide option when I press the "+" button, just the option to add a new slide which then offers me all the slides in moments to choose from.

For me it looks like this when I select a slide somewhere in the slideshow and then press the "+" button. Maybe it depends on the slideshow theme: I can add a new text slide.

Deleting the title slide is working without any problems in Photos on all my Macs in Yosemite. It is weird, that not even a new library does help in your case.

You could try two work-arounds:

1. Instead of deleting the Title Slide, enter a string of spaces as the title, so the title will be invisible.
2. Or press the "+" button to add a new title slide to replace the old iPhoto title slide. Then try to delete the new title slide, after you quit and reopend iPhoto.

The text should stay deleted. If it doesn't, make a test, if it is caused by your Photos Library. Create a new library for testing, import a few photos, then create a test slideshow. If you can delete the text in this test library, switch back to your main library and repair it.

See this help page on how to repair: https://help.apple.com/photos/mac/1.0/?lang=en#/pht6be18f93

Important: You should back up your photo library before repairing your library.

• If Photos is open, choose Photos > Quit Photos.
• Press Option-Command and double-click the Photos icon in the Applications folder (or click the Photos icon in the Dock).The Repair Library window opens.
• Click Repair to rebuild your photo library.

To create a new new library for testing see this page: Use multiple libraries

Create a new photo library

• If Photos is open, choose Photos > Quit Photos.
• Hold down the Option key and double-click the Photos icon in the Applications folder (or click the Photos icon in the Dock) to open Photos.
• In the Choose Library dialog, click Create New.
• Type a library name and choose a location to store the library.
• Click OK.

Switch between photo libraries

• If Photos is open, choose Photos > Quit Photos.
• Hold down the Option key and double-click the Photos icon in the Applications folder (or click the Photos icon in the Dock) to open Photos.
• In the Choose Library dialog, do one of the following:
  • Click the library you want to use, then click Choose Library.
  • If the library you want doesn’t appear in the Choose Library dialog, click Other Library, navigate to the location of the library, select it, then click Choose Library.

Yes, it does.