As a practical matter, if everything else is working and you do not use Subversion to manage code in a version control repository, then you can probably ignore the error. But beware of using very old SQL Developer versions with Java versions they were not intended for.
I believe 3.x went with Java 6. Probably Java 8 was not well-supported until 4.1 &up.
Does Help > About > Properties really show a java.home of jdk1.8<something>? Does your sqldeveloper\sqldeveloper\bin\sqldeveloper.conf contain a SetJavaHome line for the same? Possibly your download of 3.x came bundled with a jdk (is there a sqldeveloper\jdk\jre\java.exe in the install directory structure?) and actually Java 6 is being used.
Anyway, I suspect the real solution is get a new laptop or desktop with SSD and upgrade to the latest version!
This is what I've found
In Help > About > Properties : java.runtime.version 1.6.0_11-b03
In sqldeveloper\sqldeveloper\bin\sqldeveloper.conf : SetJavaHome ../../jdk
Is it possibile to find SQL Developer 4.1 or 4.2 ? It could solve the problem, but it is no longer available on Oracle website
Use version 20.2, if you're having issues with that, we can actually help you.
Not much we can do for software released a decade ago. Same input as on StackOverflow.
There is a "Previous Version" link on the download page for each version, but today (literally today, I just checked!) that only takes you back as far as the 19.1 release. I believe support for access to earlier versions got zapped within the last 18 to 24 months, so no joy. Sorry.
One more comment, but with regard to performance. If your Windows is 32-bit (SQL Developer runs under Java 32-bit with that bundled jdk in use; plus you say Oracle client is 32-bit), then it may just be a memory limitation most responsible for the poor performance. A 64-bit OS running on a system with solid state disk is the configuration you want.