There are many ways to make an object slow, but the most common is that calculations take a long time.
Try to identify which of your objects is the slow one. Then try adding the same data to a standard object and check if it's also slow. If it is, the problem is your calculations. If not it might be your object:
- does it make a lot of calls to engine?
- does it fetch more data than needed ? Like thousands of rows where you only see a few.