can not restore backup when backupfile is large even though backed up by same server

I use Virtualmin Pro and have been using the backup restore feature. However when it came time to restore a backup that was 1.7GB it just kept timing out. It is on a Xen VM so I decided to try different things and found out if I increased memory from 2GB to 4GB that the file would restore properly. Is there a way to make this work without increasing memory. I have several large domains and they need to be able to backup and restore especialy when the backup and restore are all on the same server.

Thanks for your help.
Bill