Wireless Joint

There is a lot of variability in the quality of antennas out there.
Next to no quality reviews and comparisons.
If you purchased a name brand antenna, you would hopefully be able to resell it if you do go fiber in the future.
Also, if you want to sell your kit in a few years, it should be 5G ...

You should explore cellmapper.net
If have an android or windows phone, use the app and map some data points.

A 4g lte signal has physical limits per your unique situation, setting the bar of Mbps.
Who knows if your 30/30 is via a simple 4G path.
With that, the only way to increase bandwidth is ...

The best bang for your buck would probably be a WG3526 router with a cat12 Sierra card inside (the pci-e one, so you don't need the M.2 adapter), the The Wireless Haven flat panel mimo antenna (15dbi), and enough lmr240 with proper connectors to hook it all up. That should come up to somewhere ...

I live in a rural area, I want to use LTE as internet source.

This is my place represented as a 5 years old kid drawing:
https://i.postimg.cc/vBQJ4kPK/home-towers-cereal.png

Distance between home and each tower is between 2 and 3 km.

I've tested on my roof with a smartphone and I can get 20-30 ...