Thank you for the tests.
I got to the history of testings and I have noticed the problem is with my mobile provider.
By the way: I was using speedtest.net for years and yesterday, for the first time, I noticed a history of test is stored for my device
It can be reached by a second left icon at the screen bottom - if somebody doesn't know like me before.
I do use Virgin Mobile in Poland which leases resources of T-Mobile and of Play - our local provider.
The speeds are very unstable.
You can see the difference between what was yesterday and today's morning - see the pictures 1 and 2.
The highest score - which I remembered - was reached with other provider, NJU Mobile - picture 3. I've bought a sim especially for data transfer when I went skiing abroad and put it in second sim slot. It was much cheaper than using roaming.
On NJU mobile there was much higher speeds than on Virgin which in fact I haven't already noticed.
3 MB/s LTE is for me acceptable. 1 MB/s or lower - is not.
I must think what to do with it.
Thanks both for Marky and Jamie for their tests.
MIUI 8.2.3 has nothing common with the low speeds of my LTE.