psi= pounds per square inch. Obviously yes, it is a function of surface area. 2x2 =4in squaredx 15psi equals 60 lbs of pressure. Compared to a little puncture @ 6-7 bar, 60 is a lot more.

Also the JB weld is fairly sensitive to proper mixtures. If it is off by enough, it will fail.

I think you should be fine with JB weld if you take your time and do it right. Scour the surface to be welded, and then clean it with Denatured Alcohol, let dry (15-20 seconds) and the weld away. You wanna clean it not long before welding to get the cleanest surface.