Here is my thoughts on your issues , 15 -15 - 15 is to much for flowering period the nitrogen part , anyways even tho N is needed in flower not as much is needed
i realize your on a tight budget but your going to have purchase some bloom nutes at any botanic store ask for tomato ferts they will do you just fine.
When entering Flowering stage you need more P and K and less N
s for your temps there fine 85 as long as you got good air movement and air exchange plants will thrive but remember warmer temps means more transpiration from plants so more watering s are needed
Your plants appear to be frying up this is from the excess build of of Nitrogen in your medium so here is how your going to fix it your going to make a batch about 1/4 strength of that new bloom nutes and flush your medium 4 times the volume of it then things should come back in order

Good luck Doc