How to debug possible wordpress memory leak?

We've published a wordpress website recently, and it has been constantly hitting the server's resource limit (1.5 GB RAM), but the thing it we're using the same plugins used on every other website we built(about 30 plugins).

Running "ps -auxwww | less" gives me this: It looks like PHP keeps creating processes that take too long to die and it's eating all the server resources (sometimes there are over 30 processes running for 30+ seconds).

The only major difference is the number of posts, we have about 30k posts and we're using WPML(https://wpml.org/), to translate them to 2 other languages (so the posts table has over 90k entries).

We're also hitting the database's memory limit. So my guess is that mysql is taking too long to respond and that causes the processes to hang for too long, it stacks up and uses all the server resources. But how can I confirm it? And how to fix it?

Thanks