When I used IDE prior to 1.6 my laptop was never fast - Non Teensy usage. I went to 1.6 with the Beta for my first Teensy 3.1 usage it didn't seem much slower to load. The IDE scans the tree on loading, after that all seems reasonable on my aging i5 under Win 7. The 1.6 update and Beta TeensyDuino may give you better results, there are some improvements for compiling.