I'm afraid there are going to be some loading and distortion issues with that design.
First, the loading. Most 150:15k transformers (1:10 winding ratio) want to see 150k at the secondary for optimum damping. By loading this one with 50k, there will be two effects. The transformer's frequency response may suffer by being overdamped, and you may get a rolloff at the top. Meanwhile, the input impedance will be 500 ohms (50k / 10^2). An SM57 would probably be pretty happy about that, but most condenser mics would not.
Second, take a look at the output. Assuming you load it wilh 600 ohms, and want to drive the output to +20dBu (that's 16dB over the standard +4dBu operating level, not a whole lot of headroom, but usually enough). +20dBu is 7.75Vrms, or about 10.96V peak. Driving that into 600 ohms requires about 18.3mA, so you'll have to operate the output tube at at least that current.
But...18.3mA across a 22k resistor drops a bit over 400V, and the plate supply is only 180V. So that's not going to fly; A resistor of 4.9k would drop about 90V at 18.3mA, leaving the cathode about halfway between ground and B+. It'll dissipate about 1.6W, so a 3W or bigger resistor would do the job.
But...at maximum output the tube needs to be swinging to about 36.6mA. How linear is the tube's behavior at current swings of zero to 36mA? My guess is, not very; the distortion will be high.
It's probably feasible to redesign the preamp for a 10k:600 ohm output transformer. That'd need only about 5mA of idle current (well, a bit more for linearitly's sake, but let's ignore that for the moment). But you'll need to crank up the B+, since +20dBu at the output means about +32dBu at the output transformer's primary. Run it at +300V, juggle resistor values, and you'll be in better shape.
Peace,
Paul