Hi Frank,
You might need to play with this a little more bit more, but adding this to your theme’s style.css file or using the Advanced CSS editor in the WordPress Customizer (Appearance > Customize) might do the trick:
/* Sets widget event title size */
tribe-mini-calendar-event h2 {
font-size: 25px !important /* or whatever size you'd like */
}
/* Sets Photo View event title size */
#tribe-events h2.entry-title {
font-size: 25px !important /* or whatever size you'd like */
}
Here is a screenshot of how that looks in Photo View when I tested it on your site. Like I said, though, you may wind up using different classnames than what I provided and need to play with it a little more to get it just right.
Cheers!
Geoff