So. I have mydata.test = -180.123451; on TX side but on RX side i see on LCD -180.123443
I try different test data, but every time i see lost of precision in last two or three sign.
Don't blame the library, it's what the chosen type offers in precision. A float uses 4 bytes to store the information, so you get about 7-8 decimal digits resolution, in total not just after the decimal point. With 3 digits in front of the point you get 4 to 5 digits after the point maximal precision. Try printing the input value on the sending side and you'll get the same output. If you need a higher precision, don't use floats (double translates to floats on the Arduino, so you cannot use them too). I'd suggest to use fixed point numbers with either 32 or 64 bit so you get the precision you want.