See newen, 15-5-5 is perhaps too much nitrogen. I use 20-20-20 at the rate of 1/2 tsp. Per gallon but once a month.
I know that those 20-20-20!numbers look like a lot but it is much less frequently applied.
Now here is a trick for you to try Pier and newen, when you see that the days are getting shorter, we are heading into fall, move your Phalaenopsis into a room for two weeks, turn down the heat in that room, close the door and open a window a little. Use a little oscillating fan to move the air. It will drop the night time temperature enough to promote spike production.
You can do the same in the spring. They need a good two weeks of lower night temperatures to initiate spikes.
64-70 should go to 55-70 and after the two weeks, see if you get bloom spikes. It may take 4-6 weeks before you see them but you will see them.
And if they were mine, I would fertilize once a month at most.
