Lofi,
Sorry that you are seeing issues with the 2015 Stable release. I could configure and deploy projects to JBoss 4.2.3 without any issues.
Can you please give us some more information?
1. What kind of project is it (web/ear/ejb etc) ?
2. If a particular project is not deployable to JBoss 4.2.3, then the deployment wizard will not display the server even though it is configured.
JBoss 4.2.3 supports J2EE 1.2,1.3 and 1.4. Please recheck the version of the your project.
3. Please create a J2EE 1.4 web project and check if you can deploy the project to the server.
4. If possible, please send us your project to help us replicate the issue at our end. You can strip the project of its source code before sending it.
In MyEclipse 2015, you can hide the sandbox Tomcat and Derby servers from the Servers view. Here is the screenshot for your reference :
Let us know how it works for you.