Premiere Elements is virtually never backwards compatible. And you certainly will not be able to open version 7 files in version 15. In fact, trying to do so will likely corrupt the project files.
We always recommend completing your project in the version you started it in.
Thank you for your reply Steve. the problem is that i cannot complete the current project under the current condition. I am not a pc expert so I do not know how to explain the problem I am having. but my pc is very slow. Pe7 opens normally. but when I try opening my saved file to continue editing, the whole program shuts down. If I open a new project, it lets me edit with no problem. I'ts as if the existing project has some error. cause when ever i try to open it, it eithers says that the program is low on virtual memory. or it crashes and just closes the program. i do not even get to render the existing project let alone save it as a file in order to open it when i intent to use Pe15 on a new pc I ordered and am awaiting to arrive. do you have any thoughts on this?
Not without knowing a lot more about your system, asharuba. Unfortunately, the issues are likely way too deep to troubleshoot on a user to user forum.