Older/lower leaves yellowing and wilting. Assuming...

I wouldn't think it would be a P def as those usually splotchy and not really spotty. It might be more along the lines of a light K def mixed with an N def as they both cause yellowing and K causes brown spotting like that. I would check your soil PH. Water till runoff when you do a normal feeding. Catch the runoff and test its ph and compare it to the ph of the water going in. If its the same as what went in you are golden and probably just need to up your nutes or feed more often. If it is significantly higher or lower than what went in(say +/- 0.5) You may have a ph issue in the soil(built up salts is the usual cause) and need to flush it. When I flush I do so until the ph in my runoff is within +/- 0.1 of my input. Once flushed you should feed with a full dose of nutrients because you will have likely pulled out any synthetic nutes that were in the soil.