Select Battlefield 3 in the drop down box (If it's not there click add and find bf3.exe located C:\Program Files (x86)\Origin Games\Battlefield 3)
Find Threaded optimization
Turn On
Click Apply
You should now have fast load times when changing maps
AMD/ATI Cards
Download ATT
Install
Right click on the icon in the bottom right corner of your screen
Click on Tweaks
Click on Advanced Tweaks
In the drop down box select Multi Threaded Support
Change to 2 or 4 (Depending on how many cores you have on your CPU)
Make sure the radio box above is ticked
Click apply
This should fix it for you