Website loads fast on Desktop but REALLY slow on Mobile

Hello, hopefully someone can help me with this problem…

I’m building up a website and for some strange reason that I have not been able to figure out, the site loads fine on PCs/Mac but extremely slow on tablets/mobiles.

I’m using Spacious (child theme), the theme is responsive and I have the following Plugins installed:

Accordions, AddToAny Share Buttons, All In One SEO Pack, BackWPup, Category Order and Taxonomy Terms Order, Column Shortcodes, Contact Form 7, Contextual Related Posts, Easy2Map WordPress Plugin, Google Analytics Dashboard for WP, Heroic Favicon Generator, Instagram Feed, Lazy Load, Maintenance Mode, Media Library Categories, My Page Order, P3 (Plugin Performance Profiler), Pretty Link Lite, Recent Posts Widget With Thumbnails, Snazzy Maps, Sub Categories Widget, Tabs Responsive, W3 Total Cache and WP Smush

And this is what I have tried:
*Deactivated all plugins and activate one-by-one.
*Cleared WP-Cache.
*Tried different devices, browsers and internet connections.
*Cleared browser caches.
*Ran speed tests online.
*Optimized Database.
*Reset .htaccess file.

The website loads quite fast (less than 5 seconds) on a desktop computer but specially on mobiles, it takes sometimes 15 seconds, sometimes more than 45 seconds to load or does not load at all. Any idea what can be causing it?

Website: https://www.trimati.com

Any comments would be highly appreciated. Thank you!