There is a setting in DVDFab->Common Settings->DVD to Mobile called "Memory amount to be used for converting" with a drop down selector. The default is "Auto" I think, you may want to try some of the other settings to see if you can optimize for your system. With DVDFab in general you will get the best performance if you configure your system to avoid internal bottlenecks, e.g. don't have the read optical drive and the Target hard drive on the same controller. Avoid multitasking, especially when doing mobile conversions. The CPU is very busy--look at it on the Performance tab of Task Manager. All that being said, the wmv profiles do all seem to be slower than most of the others. Use the smallest screen size you can get by with, it will make a difference. And Complication's point about power is well taken--most laptops' power management throttles back the CPU when running on battery power, so always connect the AC adapter.
The Mobile option has its own sub-forum now. Try it next time, the developers look there first for mobile issues.