How to use the same antenna to receive and transmit on the same frequency with an SDR [Half-Duplex]?
You might want to change your title as it implies that you want simultaneous transmission and reception, half-duplex is way easier to achieve. 

Now, even for half-duplex, 47dBm TX power with a -15dBm RX limit is a difference of >60dB (or one million to one power ratio) so what ever solution you use needs good isolation. 

With a good PIN diode switch and with the LNA powered down while the transmitter is operational (and real good shielding, but that goes without saying), that'll give you a reasonable amount of isolation between TX and RX.

Failing that, a good RF relay, but all this assumes half-duplex, if you decide you want full-duplex then that's a whole other can-o-worms!