Yes, this is possible: one can customize the look of all slideshow tools by adding a few lines of CSS to the page that contains the slideshow tool.
To open the "raw CSS" editor:
1. go to the pages tab
2. click on the pencil icon
3. go to style tab
4. scroll down to "raw CSS"
5. paste the following lines:
#exposition-content .tool.tool-slideshow .icon {
display: none;
}
#exposition-content .slideshow-nav {
display: none !important;
}
this hides all the controls.
One can change the speed or even timing per slide, by double clicking the tool -> options > automate.