@anthoooo The cURL error 28 literally means that your site tried to perform a request using the cURL library but the specified timeout period was reached before getting a successful result for the request.
Could you please try to add following rules to your .htaccess file and check speed of your site?
# BEGIN WP-Optimize Gzip compression
<IfModule mod_filter.c>
<IfModule mod_deflate.c>
# Compress HTML, CSS, JavaScript, Text, XML and fonts
AddType application/vnd.ms-fontobject .eot
AddType font/ttf .ttf
AddType font/otf .otf
AddType font/x-woff .woff
AddType image/svg+xml .svg
AddOutputFilterByType DEFLATE application/javascript
AddOutputFilterByType DEFLATE application/rss+xml
AddOutputFilterByType DEFLATE application/vnd.ms-fontobject
AddOutputFilterByType DEFLATE application/x-font
AddOutputFilterByType DEFLATE application/x-font-opentype
AddOutputFilterByType DEFLATE application/x-font-otf
AddOutputFilterByType DEFLATE application/x-font-truetype
AddOutputFilterByType DEFLATE application/x-font-ttf
AddOutputFilterByType DEFLATE application/x-font-woff
AddOutputFilterByType DEFLATE application/x-javascript
AddOutputFilterByType DEFLATE application/xhtml+xml
AddOutputFilterByType DEFLATE application/xml
AddOutputFilterByType DEFLATE font/opentype
AddOutputFilterByType DEFLATE font/otf
AddOutputFilterByType DEFLATE font/ttf
AddOutputFilterByType DEFLATE font/woff
AddOutputFilterByType DEFLATE image/svg+xml
AddOutputFilterByType DEFLATE image/x-icon
AddOutputFilterByType DEFLATE text/css
AddOutputFilterByType DEFLATE text/html
AddOutputFilterByType DEFLATE text/javascript
AddOutputFilterByType DEFLATE text/plain
AddOutputFilterByType DEFLATE text/xml
# Remove browser bugs (only needed for really old browsers)
BrowserMatch ^Mozilla/4 gzip-only-text/html
BrowserMatch ^Mozilla/4\.0[678] no-gzip
BrowserMatch \bMSIE !no-gzip !gzip-only-text/html
<IfModule mod_headers.c>
Header append Vary User-Agent
</IfModule>
</IfModule>
</IfModule>
# END WP-Optimize Gzip compression
# BEGIN WP-Optimize Browser Cache
<IfModule mod_expires.c>
ExpiresActive On
ExpiresByType text/css "access 28 days"
ExpiresByType text/html "access 28 days"
ExpiresByType image/gif "access 28 days"
ExpiresByType image/png "access 28 days"
ExpiresByType image/jpg "access 28 days"
ExpiresByType image/jpeg "access 28 days"
ExpiresByType image/webp "access 28 days"
ExpiresByType image/x-icon "access 28 days"
ExpiresByType application/pdf "access 28 days"
ExpiresByType application/javascript "access 28 days"
ExpiresByType text/x-javascript "access 28 days"
ExpiresByType application/x-shockwave-flash "access 28 days"
ExpiresDefault "access 28 days"
</IfModule>
<IfModule mod_headers.c>
<filesMatch "\.(ico|jpe?g|png|gif|webp|swf)$">
Header set Cache-Control "public"
</filesMatch>
<filesMatch "\.(css)$">
Header set Cache-Control "public"
</filesMatch>
<filesMatch "\.(js)$">
Header set Cache-Control "private"
</filesMatch>
<filesMatch "\.(x?html?|php)$">
Header set Cache-Control "private, must-revalidate"
</filesMatch>
</IfModule>
#Disable ETag
FileETag None
# END WP-Optimize Browser Cache