There's no way to know what's wrong -- no useful information.
But if you're running AE CC 2015, you should know that the way it previews has changed, and you need to read up on it.
As far as "information" what kind of information would you like me to add to my post?
And, yes sir, I am running 2015.2 release Version 13.7
I already read about the changes that came with the latest update.
It does not recommend any settings to be changed or what should be selected in the Preferences. It just says they are not using the word "Ram" for preview anymore and we can continue working on layers etc. while the preview is in progress or we can alt+drag the cti during a preview now....
Non of those "what changed in the new release" is helping me.
I honestly do not know how else I can describe the issue. Again, I am making a change in one of the layers, than hit the play button then for me to preview a project of 30 seconds long, it takes 15 minutes for the whole thing to play. It is not playing smooth, it is running frame by frame.
It has to build a cache first before it can play back.
I've had projects where it took over a minute just to render one frame. It sounds like your preview is rendering into the cache at one frame per second. That might be perfectly normal. It all depends on the contents of your composition.
Have you accidentally turned on the ray-traced renderer? If so, turn it off.
When you say it acts differently on the computers at school than the computer at home, can you please be more specific on what you mean by "different"?
Do you know the specs of those machines at school? What version of AE are they running?
First of all thank you Szalam.
As you can tell, I just started learning AE.
Under which menu is that ray-traced renderer?
As far as the school computers, they have the same ram as mine, graphics card is a lower model than mine, and AE is 2015.0 release version 13.5. And by different I tried to mean, it does not preview as slow as what I am experiencing at home. If I make a small change (scale, position etc. with one layer) as soon as I hit play button for preview it plays it just fine and fast whereas at home I have to wait for minutes. And also, if I drag the cti at school all my layers are visible, I can see what changes I made or just see the objects but at home when I drag the cti with the mouse I only see their outlines until after a certain time, they all show up.
I apologize for describing poorly and with child like terms. Like I mentioned I am new to the whole thing and these are the best descriptions I can give at this point with my current knowledge.
Thank you for your valuable time and help by the way.