The ingame world is not preloaded in the editor. If you use the "Preview" in the editor multiple times, it loads the map every time, resulting in very long loading times. It becomes a huge issue when one needs to use "Preview" multiple times in short period of time, like when one is e.g. tweaking script or object position that is very common. It has a severe negative influence to the development.
- Legacy ID
Open editor in the game, place a character on the map and click "Preview". When the world is loaded and you appear in the game, select "Abort" and click "Preview" in the editor again. The map will load again at least about 10 seconds, unlike in Arma 2.
The preview mode in the editor should be made similar to Arma 2, where the map had to be loaded only once, and after that you were able to join the ingame world almost instantly with the preview.
JNC - yes it is, if you are tweaking something, e.g. object position, because you have to switch between the preview and editor again, again and again. What could be done in Arma 2 in minute, can take up to 10 minutes now. Think about e.g. a regular mission maker who has to repeat this procedure tens, even hundreds of times. It can result in hours of completely wasted time pretty fast. Hence the ticket.
This should be really fixed or the upcoming user-created content, especially missions will have remarkably lower quality and be remarkably simplier than what they could be. I was testing a single depth gauge script (a really really simple one), and having to load the map again, again and again already made me frustrated. Just think about what kind of hell it'll be with large missions...!
I believe that this issue is a duplicate of http://feedback.arma3.com/view.php?id=95 (read the notes).
TLDR version is that this will only happen if the players unit is armed with MX series of rifles or SDAR. Try spawning as OPFOR rifleman (which is armed with the Katiba instead of the MX/SDAR), which should result in a speedy load.
I've created a similar case: http://feedback.arma3.com/view.php?id=3221 .
This case 3044 talks about the editor; but I see the same behavior with the editor and when loading a save game quick in succession.
From my view it looks like in both cases it's the same issue behind the scenes.