We have a costumer that have 3 stores with different databases. In every store has a wildfly running some webservices which communicate between them. Each json request with 10/30 rows spends 1 seconds in average. Every wildfly uses 1,5 gb of RAM. I know that memory is always a problem in Java, but can I be more economic using some microframework like Javalin or microservices rather than a java ee app server? And node.js would be a option for better performance?
Before you start looking into a different architecture, which would probably make for a major rewrite, find out where all that time is going. Set up profiling on the WildFly servers. Start by doing that on one, then have some calls coming in. Check how much time is spent in various parts of the stack. Is one call to the web service handled rather slowly? Then see where that time goes. It might be the database access. Is one such call handled pretty quickly on the server itself once it comes in? Then your best bet is your losing time on the network layer.
Check the network traffic. You can use Wireshark or a similar tracing tool for this. See how much time actually passes between a request coming in and the response going out. Is that slow but the processing on Wildfly itself seems fast enough? Maybe there's some overhead going on (like security). Is the time between request and response very fast? You're definitely looking at the network as the culprit.
Eventually you may need to have profiling and network tracing active on all three servers simultaneously to see what's going on, or for each combination of two servers. It may turn out only one of them is the bottleneck. And if you have servers A, B and C, from the sound of it your setup might cause a call from A to B to also require a call from B to C before some result can be returned to A. If that is the case, it's little wonder you may see some serious latency.
But measure and find the root of the problem before you start deciding to change the entire framework and a different programming language. Otherwise you may put a lot of time into something for no improvement at all. If the architecture is fundamentally flawed you need to think of a different approach. If this is still in the prototyping phase that would be substantially easier.