In this thread I will list ways to improve the preview times of construct 2 projects.
1. Change your preview browser.
Using lots of animations frames can DRASTICALLY increase preview times, even if you don't have any events!
So if you have a sprite with lots of animation frames like this example: dropbox.com/s/4fphcl68artl6jm/long%20preview%20times%201.capx
or if you have many sprites with very view animation frames like this example: dropbox.com/s/cmhz198rkan8eyu/long%20preview%20times%202.capx
Your game can take a long time to preview. But changing your preview browser can reduce preview times greatly.
Surprisingly, Internet Explorer and Microsoft Edge preview much faster than Chrome and Firefox for me.
2. Uncheck preload sounds.
This can decrease preview times if you use a lot of sound effects. This doesn't affect music files though.
If you know of any other ways to decrease preview times please let me know so I can add them to this list.