This sounds high, but... PPMx What?!
If it's 1500ppm "500" (Tds), that's 2100ppm 700 (ECx700), that's 3EC.
If it's 1500ppm "700" (ECx700), that's 1100ppm 500 (Tds), that's 2.2EC. That could be reasonable. The top would be pretty high.
Op, always easiest to give your measurements in the universal EC.
Either way it's high (considering you're posting in the newbie section). I was growing tree's in a cch20 and never getting near that high.
Now here's the learning question to ask yourself; Why did you decide to raise the nute strength?