Below I consider the characteristics of the neophyte pawn.
1) In my opinion, blood pumping can be reduced by 2 times. Reduce total blood pumping from 350 to 200%. This will slow down the pawn speed.

2) Reduce the bonus to breathing from an multi-lung from 50% to 25%.

3) Ossmodula and Biscopea moving bonus reduse from 25% to 10-15%

Marines Pawns will run fast, much faster than normal pawns, but it will not be TOO fast.

I think that need to reduce organs health from 600 to 60-100.
Organs now have too much health. They are almost impossible to destroy.
In fact, SM organs were often destroyed.

Should they really become Primarchs at the full 19? Seems a little OP. There should be some intermediate stage that stops them before then. Perhaps locked behind a research option and requiring either A lot of genes seed for a single implant or Trial/Error. Like a task pawns can work on, and fail a lot at, before finally getting an item to upgrade and Astartes to Primarch level.

how long should it take for it to develop

Betcher's Gland is getting kind of annoying. My melee pawns bite more often than using their ♥♥♥♥♥♥♥ massive laser swords. Wouldn't be that big a deal if the cooldown on it wasn't so long. Because of it, my pawns take a long pause after every three attacks and battles take longer than they should. I reduced the damage of the Betcher's Gland to 0 in the mod's menu, but it didn't do anything, still doing around 10 damage, still makes pawns bite more often than they swing.

Replace lifting capacity with work.

I think lifting is good but they move just too fast (maybe a mod setting to change that for everyone) idk how much work would it take for you