Handling more websocket connections
Welcome to code review community. Few initial thoughts, when writing python code; following PEP-8 style guide makes your code more maintainable. Which would amount to (but not limited to):

Functions and variables named in lower_snake_case.
Avoiding whitespaces in function parameters/arguments.


Moving on, you can put your websocket handling code in its own submodule. For eg.
class WebSocket:
    def __init__(self, url):
        self._url = url

    def close(self, ws):
        # handle closed connection callback
        pass

    def connect(self):
        self.ws = websocket.WebSocketApp(self._url, on_close=self.close)
        self.ws.on_open = self.open  # for eg.
        self.ws.run_forever()
    .
    .
    .

If you want it to support threading, you can extend this class with threading.Thread sub-classing (you may also choose to subclass multiprocessing.Process later):
class ThreadedWebSocket(WebSocket, threading.Thread):
    def run(self):
        # This simply calls `self.connect()`

this way, if you want to initialise threads:
url1_thread = ThreadedWebSocket(url=url1)
url1_thread.start()
url1_thread.join()

The subclassing is mostly a matter of preference.

In the on_open callback, you are dumping a dict to json and then inserting it to a string template. The following achieves the same result, and is more intuitive (imo):
def on_open(ws):
    def run(*args):
        subs = []
        trade =  {
            &quot;method&quot;: &quot;SUBSCRIBE&quot;,
            &quot;params&quot;: subs,
            &quot;id&quot;: 1
        }
        ws.send(json.dumps(trade))


Coming to your question about library alternates, and performance, network I/O is generally a blocking call. This was one of the major reason I suggested going with the websockets package. The other being; we've been using websockets at our organisation for over an year in production. And it has been working really impressively for us, handling a throughput of few GB data everyday with a single low-tier machine.