Hello,
for the requirements described we can recommend the following:
1. Basic Edition license used with two Kinect v2 sensors setup:
http://docs.ipisoft.com/User_Guide_for_Multiple_Depth_Sensors_Configuration2. Biomech Add-on:
http://ipisoft.com/store/ipi-biomech (used to get joints coordinates)
3. System accuracy depends on many factors. But specified accuracy (1.5 cm) looks feasible to our system. You can check publications that include comparison of iPi with other systems, listed at the bottom Biomech Add-on page linked above.