no help from WordPress
that is not surprising, as your issue is not really general WordPress related:
– how to work effectively with browser inspection tools is outside of this forum …
– any specifics to your theme are outside of this forum …
twentyfifteen was developed by the folks at WordPress … where would I go if I wanted to alter the styling for the title text on a static page?
either looking into the code of page.php (and whatever template parts are getting called from that code) or looking into the output of a static page in your browser (‘view source’ on the browser tool bar) or using a browser inspection tool, you would find how the title of a static page in Twenty Fifteen is formatted:
– relevant code from content-page.php (which is called from page.php):
<article id="post-<?php the_ID(); ?>" <?php post_class(); ?>>
<?php
// Post thumbnail.
twentyfifteen_post_thumbnail();
?>
<header class="entry-header">
<?php the_title( '<h1 class="entry-title">', '</h1>' ); ?>
</header><!-- .entry-header -->
<div class="entry-content">
– relevant section from the html of a static page in the browser:
<article id="post-2" class="post-2 page type-page status-publish hentry">
<header class="entry-header">
<h1 class="entry-title">Protected: Sample Page</h1> </header><!-- .entry-header -->
<div class="entry-content">
– screenshot of Firefox right-click ‘inspect element’ tool:
https://imgur.com/9Qfhwmb
– alternative, using Firefox’ web developer add-on ‘CSS’ ‘display style information’ would give you a whole hierarchical list of the CSS files and lines where any relevant formatting of teh inspected element origines.
you would then use this information to write a new CSS style either into style.css of a child theme or via a custom CSS plugin;
in this case (Twenty Fifteen):
.entry-title { }
or more specific:
.entry-header h1.entry-title { }
or even more specific:
.page .entry-header .entry-title { }