Opening a big memory snapshot sometimes takes a lot of time. Usually it is normal due to the fact that some complex calculations are to be made by the profiler while loading the snapshot.
Still you can use the following solutions to make snapshot opening faster.
If possible, open big memory snapshots running the profiler UI on a 64-bit system. The reason is that snapshot opening is a memory hungry operation, thus you would benefit from 64-bit processing capabilities.
In any case while loading the snapshots, try to avoid simultaneous running of other applications which use much memory. Running several applications may cause active disk swapping that leads to overall system performance degradation.
For the same reason, consider using a machine with more physical memory (RAM) available.