I am planning to install an LTE router in my apartment, since there is no cable access. There are two LTE towers in the vicinity, one is 1150m (3770ft) away, the other 2550m (8370ft). Both have a line of sight with my apartment, and are about 2° apart as seen from the apartment.

Before I decide to even buy a router, I would like to know if a router (optionally with an external antenna) might solve the problems I currently have when using my mobile phone as a hotspot, namely

* the connection gets pretty slow in rain. This means my cellphone shows fewer "connection bars" and the internet speed decreases.
* the connection gets slow in the evening. While the "connection bars" stay, the internet speed decreases.

I'm sure there are a thousand reasons for this, many of which I don't even think of. Is there a way to troubleshoot the current connection, to know if the problems are caused by interference, or too many subscribers, or just the usage of the small antenna in my cellphone, or something totally different?