With the latest update to NX, JT assemblies and components can now be loaded Minimally. All multi-CAD workflows will benefit from this level of performance improvement. On average the load performance of JT assemblies has been improved by approximately 3X native & 9X managed modes.
The load experience is enhanced by dynamically loading parts throughout the load process and supporting user interaction during loading.
After the load is completed NX will seamlessly load additional data as required by the user’s interaction
See here for a demonstration on the performance of JT Load: