Yes, you’ve chosen a body font (Crimson Text) that is naturally small as part of the font design.
The WPBakery Page Builder plugin doesn’t enable you to customise fonts for buttons, but you can tweak the fonts for buttons with some custom CSS.
If you use Internet Explorer, Chrome, Firefox, Safari or Opera you can use the browser’s built-in developer tools to point at and “inspect” elements on a web page to find out what styles they use. You can even tweak the styles live to experiment with any changes you might fancy…
So the custom CSS you’d need is this…
.vc_btn3.vc_btn3-size-md {
font-family: "Open Sans";
font-size: 20px;
}
Go to Appearance > Theme Options > Custom CSS and add that CSS to your Custom CSS box. Adjust the values to suit your specific situation. Naturally, the “Open Sans” font must already have been loaded in order to use it.
Thanks.
References:
https://www.w3schools.com/cssref/pr_font_font-family.asp
https://www.w3schools.com/cssref/pr_font_font-size.asp