I think that since she's on the low end of average, she can take small buffs like this without needing a nerf. They're pretty small buffs unless you're playing in a high-ping environment. Compensation nerfs aren't needed because she isn't strong enough to justify them.
When I get to play with 60 or 40 ping, I can instantly detonate the E. It would detonate almost imperceptably quicker if I could predetonate it. Not enough of a difference to justify a nerf. Any change you gave to the projectile speed would make it harder to hit than it is right now. She doesn't need that power decrease.
I'm guaranteeing you, this change isn't going to push Lux over any boundaries. She can get the buffs and nothing else, and she'll still be perfectly fine.