JP15 stiff strings feel

I use 9-42 strings on my jp15. Tried a couple of different ones from different manufactures but they all feel stiff compared for example to my RG with edge tremolo. My action is pretty low(1.2mm on e, 1.5mm on E, or even lower), neck is almost straight. Saddles are not flat(parallel) with the body, they are pointing upwards. Should they be parallel with the body and could that be the problem? How about spring tension, maybe changing tremolo springs to a softer ones?