Normal cherry-standard springs are 15mm. Longer springs like the 16mm ones are used to make the force required more consistent all the way through the press. It’s a bit hard to explain, but basically shorter springs will be lighter at the very start of pressing the switch and gradually get heavier as you near the bottom. This is why force graphs for linear switches resemble a straight line with an upward slope.
When you put long springs in your switches you’re “pre-loading” the springs; they are always slightly compressed. So you end up with a force graph slope that’s closer to a flat line, and a more consistent feeling switch. In order to make 70g springs for multiple lengths you just need to make sure the force graphs intersect at the point of actuation; 70g at 2.3mm depth.
In other words, it’s down to preference. Personally I think long springs are great and you should try them out, but feel prepared for them to feel a little heavier than you might expect. But if you want a more “bouncy” feeling you should probably stick with 15mm or go down to 14mm.
If you want a more thorough explanation definitely go check out this post: About Springs