Tomcat 5.5 is compiled and runs well under
Java 1.5.
Your servlet, bean, and custom tag code should run fine with 1.5 features.
Starting with version 5.5 Tomcat ships with the JDT compiler (by the folks at Eclipse) for compiling JSPs. The advantage of this is that you no longer need a full JDK in order to run a JSP app under Tomcat.
One issue, however, is that JDT doesn't yet support all of the 1.5 features of Java.
One workaround is to configure Tomcat to use Sun's compiler.
See the Tomcat documentation for doing this.
A better workaround would be to move all of your Java code out of the JSPs and into your servlets and javabeans.
http://www.google.com/search?hl=en&q=JDT+Jasper+1.5+generics+Tomcat+&btnG=Google+Search