Maple products in Canada sells poppets which fit my P35s and bullshark, I think they will fit your P15. I get a few less fps with them, I think it is because they do not have a radius in the steel part where it meets the plastic. But they work. I did not need to lap the one I tried to get it to work.
If the shafts of the ones you have is the right diameter, the shaft can be cut to shorten it with a cutting wheel in a dremel tool. A grinder can fine tune it. If the plastic part does not seal to the valve you can use a little valve grinding compound to grind the plastic part into the valve with the valve part that goes onto the spring in the jaws of a drill. I use high speed and a minute or two of grinding plus about the same amount of time with JSB bore cleaning paste has worked several times for me now. If the head or the part that goes into the spring is too big you can reduce the size with a sanding block turning the plastic part with a drill.
If you know how to post links, could you post one to the ones you find on aliexpress? I've tried finding them there and not been successful. Even if they require fine tuning they could be useful.