I have had the same problem. we use 12.5... with 3 gig of ram pentium d 2.8 gigahertz.
We would be happy to have a 2 to 5 min update but it runs out of memory and never finishes. It's a 2 story house, we want to eventually do 3 story commercial buildings. How are other companies doing large projects if I am straining at a 2 story house?