I am have a problem with fps settings. In Lightroom I set the fps to 15 on the left but the popup on the right sets it in the 20's . How do I fix that.

For the low fps use the exactly double in video export.
when using 15 in slideshow go to 30 in video,
for 12.5 use 25.

But Robert, why are you still exporting via the Slideshow module?? You have a LRT3 license, go to Library, Grid View (G), Select the whole sequence and go to "Export". On the left side you will find the new LRTExport plugin. Chose it and get lucky!!