You don't have a lot of resources (RAM/CPU) in use so it is possible that's the constraint but you have a real learning opportunity to understand better how your tech stack works and learn some performance tuning. Your cloud provider should have some stats for you to see if those things are hitting limits, some simple charts to glance at would at least give you an idea.
You mention its a CRUD app so first thing I would look at and spend time on is your SQL queries and analyzing them. The majority of the time in web requests for CRUD apps is in the DB - because it could be loading and reading a file from disk (where the DB stores data) which is typically slower than receiving bytes on a network socket. Learn what `explain plan` means for your database flavor. I am going to venture a guess that you may not have database indexes on some tables. An explain plan for your queries should tell you what indexes, if any, are used.
For your front-end you could look into caching services for any JS framework libs, images, etc. assuming there is a way to do that on your network in China. That would reduce the bandwidth usage and if those services work properly, your end users would be downloading those assets from a faster server than you provide.