Had the same issue with my S&W PPK. I tried going to a 17 lb spring and yes it made it easier to rack. Just keep in mind there is a reason for the 20lb spring. The best thing I did to make it rack easier was to get a hand/grip exerciser to beef up my hands. I will say the PPK is an easier rack than my Ruger LCP, mainly as there is more to hold onto with the PPK.
In a previous thread on this topic someone mentioned to manually pull back the hammer first.
Think of it this way.
First, Don't try holding the guy at full extension. WHILE MAINTAINING PROPER MUZZLE DIRECTION, pull the gun close to your chest, where you have more power.
Second. Ask yourself, "Do you "Pull" a lawnmower, or do you "PUSH" a Lawnmower?"
The grip has more than surface area than the slide.
Grasp the slide in your weak hand, and "Push" the grip with your strong hand.