A 64 bit machine can handle significantly larger and more complex files than a 32 bit machine. The warning is because a 32 bit machine may not be able to handle it.
That said, most people here work on files, even 'large' ones that are not a problem on 32 bit machines.
I have had no problems opening such files on 32 bit, but then again I am not rebuilding Hong Kong
Go ahead and open it.
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"