Old thread. Here are my 5 cents.

Found the SimObjects\IVAO_MTL folder left after removing IVAO client with 2.3Gb of traffic crafts.

After removing the load time decreased from 40 sesc to 12.

Try "Scenery Config  Editor" and turn off all addon scenery, leaving only the "Basic Scenery". If this is the culprit, you might want to use SCE to load only the scenery you need for your flight.

Three years after asking the question I am guessing the OP has moved on.