The preview is very labor intensive for your processor, especially when there are effects, multiple images, music, enhancements, etc.
You can make the preview smoother by lowering the quality of the preview.
Lower the preview quality by clicking on the icon 4th from the right, under the preview screen.
Also, rendering/producing is going to be slower as you add more effects, etc.
HP Envy Phoenix/4thGen i7-4770(4@3.4GHz~turbo>3.9)
Nvidia GTX 960(4GB)/16GB DDR3/
Canon Vixia HV30/HF-M40/HF-M41/HF-G20/Olympus E-PL5.
Tape capture using 6 VCR, TBC-1000, Elite BVP4+, Sony D8 camcorder with TBC.
https://www.facebook.com/BarryAFTT