Arcosdad - Sorry to hear about your bad luck with the JW15. No question they are a bit rough.
One thing that MAY have helped with the bolt on the first one would be to screw the sear adjustment screw in (clockwise) so it sticks out more. That decreases sear engagement (pulls the sear down). They look like they are almost all the way screwed in, but there is quite a bit more screw in there. You can adjust the trigger down to a very clean break, but you can also overdo it so the sear doesn't catch.
With your second rifle where you couldn't close the bolt, I'll bet the stock was the culprit. I ended up buying a second one recently (and yes, I have questioned some of my decisions), this one a compact. When I took it apart to clean it, put the bolt in to cycle and test, it was fine. Putting the stock back on kept the bolt from closing completely. A few swipes with a dremel in the bolt handle cut-out cleaned that up right away.
My issues with the JW15 were more with the mags. They are very tight on the inside, so the followers don't work well. They tend to stick and not push rounds up. Taking the mags apart and cleaning up the inside dimensions works well. Shouldn't be necessary, but hey, China. CZ magazines also cure the problem.
It is a shame, they are a simple and robust design, and the accuracy with the 24" barrel one is not bad. I shot several 5rd groups (SK Std) at 100 to try it out. Had a couple 1 5/8" groups with the worst at 2". Once the rifles wear in a bit they are quite nice to shoot too. I don't think I ever got that kind of group out of my Scorpio.
Good old Chinese sproting rifles...a project in every box.