For performance issues you can check for below details

1)What time you see the slowness .

2)Do you observe any thread dumps during that period try to analyse that ,also you need to check multiple thread dumps to find a pattern .

3)Check the alert logs and see what are all the alerts occurring at that time and whether it have more KPI over threshold values .

4)Whether garbage collection is happening properly ,how good is your GC mechanism .

If it’s an infrastructure related issue that means if your application size is large then whether you need to increase your heap size .

Although performance issues can be caused by multiple reasons  above steps at least give you a basic idea to investigate .

Thanks,

Arun