Video is way to fast after being rendered and exported

I am using After Effects, version 14.2.1.34.

I have created a motion graphics video, using only images from illustrator, etc. I have automated and edited the entire thing. When I went to export the composition, the final result looked like it was about 2.5 times faster than the actual speed. I thought it might have been a glitch, so I restarted everything and checked the settings and tried again. I was exporting to a lossless avi.

Just now, I realized that my 'preview' (that I was basing my edits on) was in a 15 frame rate, not 29.7 as my composition is set. I am hoping to God that editing and animating- based on a preview in a slower frame rate-  won't screw up all of the hard work that I just put in... but I am not sure if this has anything to do with it.

I decided to try and export it based on a 15 frame rate, but it still came out just as quickly. I also tried to copy and paste the content into a new composition (set to a 15 frame rate), and still isn't working.

I changed my preview to 29.7 fps, and the result is exactly what I am getting in my export. Please tell me there is a way to fix this without losing days of work!!!

Is there any way to render exactly what I am seeing based on the 15 frame rate preview? That speed is perfect and the quality is just fine.