Effects of impedance mismatch on RF signals from antenna
The mismatch attenuation will only be 0.177 dB. Not much.

However, a 50 ohm LNA is designed to operate in a 50 ohm system. It will provide the specified noise figure for a 50 ohm input only! With 75 ohms input, the noise figure will be something else (worse) than stated in the datasheet. This  leads to loss of sensitivity, but with the data you have provided it is impossible to say how big of a loss.