Change your 10k pull-ups [R1 and R2] to something more like 4.7k or even as low as 2.2k. This may speed the thing up.
An ordinary bipolar NPN would work pretty well...
But the logic is inverted.
No, it's not.When emitter is pulled down (LOW) by the 3.3volt pin, the transistor is conducting,so the collector is also LOW
I still don't quite understand why 2n7000 is so often used for 3.3-5V level conversion in i2c bus lines but does not work with ws2811 signal conversion. Data rates are if anything lower, and currents are also small.
Something like this.The 'low' will be at about 0.2-0.3v, but ought to do.
Changing R1 will make no difference. Try reducing R2.