Hello ehan27 and welcome to the ArtRage forums 
How fast a tool performs in AR is mostly governed by the speed + number of cores the CPU has.
I've never owned the Lite version but I don’t think there should be any difference in any Tool’s performance between the Light version of AR and the full version.
The differences only being which elements of the full version have bean left out of the Lite one I think.
Odd that it should only be effecting one knife though. It may be a bug in the Lite version possibly.
Which Pallet Knife are you finding slow?
Is it an existing Preset?
If not what settings are you using for it when it slows down?
And how big is the canvas, i.e. Hight in pixels x Width in pixels?
Maker Of Replica Macoys
Techie Stuff:
ArtRage 6.1.1 ~ 15" Macbook Pro ~ macOS 10.15.7 ~ 4 Core i7 3.1GHz CPU ~ 16GB RAM ~ Wacom Intuos4 M