What you're saying does not make any sense. I am guessing that you split a layer so you have two copies then you set the endpoint of the second layer down the timeline about 15 seconds. Then I am guessing you grabbed the outpoint and drug it back to the out point of the layer below instead of grabbing the whole layer and sliding it in the timeline.
On a single layer you can set an in and out point only. If you want to take 15 seconds out of the middle then The easiest thing to do is to split the layer twice. Delete the middle section and reposition the second layer by clicking and dragging the center of the layer with the selection tool.
I do not think that you understand the proper use of After Effects. 90% of my compositions are 7 seconds or less and are only one shot. You should be doing your editing in Premiere Pro. After Effects should only be used to create motion graphics or visual effects you cannot create in an editing progeam. Only on rare occasions when you can't do it any other way should be you be creating a sequence in AE. Just way too inefficient.
Sometimes projects like lyric videos are done in After Effects. The most efficient way to handle that kind of project is to divide up the voice over into sentences or short paragraphs and make each one of those a separate composition. To someone new to AE this seams inefficient and a lot of extra work but it is actually by far the most fasrest and the best way to work on a project that is longer than a few seconds. Final editing audio mixing is much easier to handle in a nonlinear editor. Using After Effects as an editor is about as easy as driving a nail with a screwdriver. You can eventually get the job done but it's not very elegant.
Thank you very much for your answer . To clear it up, just incase i explained it wrong. I have a 20 second clip. I make to split points in the middle and delete whats in between the split points. Then when i drag the two part together , they play normaly asif i didnt delete the part. I will try the numorous things you stated . Thanks again
If you are working in a composition and you are starting with one layer when you split the composition using either Edit>Split Layer from the menu or the keyboard shortcut Shift + Ctrl/Cmnd + d you will end up with two layers. Split again and you have three.
If you have the selection tool (keyboard shortcut v) active and you select the middle layer by clicking on the Source Name in the timeline or the colored part of the layer you can delete it leaving a hole.
The next thing you would do would be to click and hold between the in and out points of the layer you want to move and drag it toward the out point of the other layer. If you hold down the shift key when you drag the selected layer's in point will snap to the out point of the other layer.
These are AE basics. You must spend a little time studying up. I suggest you start here: Basic AE. I also suggest that you get in the habit of using the Search Help field at the top right corner of After Effects. To learn more about editing layers type "editing layers" in the search field and you'll find a bunch of community resources on the subject.