Delay in approval cycle

[abhaytak]

We have set up a workflow for 8 stages, every stage is having some activities like status change, email notification, approval assign activity, approval actions.
But if any stage is having only status change then the workflow is working very fine but when it comes to email notification and approval assigning that time workflow is getting very slow sometimes the process is taking more than 30 minutes.

The above image is running very smoothly after this stage I am having another stage which is assigning activities and going notification by email I am attaching that screenshot below.

Please help me to identify the issue and let me know if you want any more details.